Delivery of twin pregnancy

Twin Pregnancy: Answers from an Expert

Reviewed By:

When you’re expecting twins, you know you’ll need two of everything for your registry. But what about staying healthy during your pregnancy? Do you need to double your food intake, weight gain and visits to the doctor? With regard to the babies, are there two placentas and two amniotic sacs, or can they share these?

 Johns Hopkins maternal-fetal medicine specialist Jeanne Sheffield answers eight commonly asked questions.

1. Do twins share a placenta and an amniotic sac?

   While some twins may share a placenta and an amniotic sac, that is not the case for the vast majority of pregnancies. Here are three major possibilities that exist:

   • Two placentas and two amniotic sacs. A twin pregnancy with two placentas and two amniotic sacs is the optimal twin pregnancy, as each baby has its own nutritional source and protective membrane.
   • One placenta and two amniotic sacs. In pregnancies with one placenta and two amniotic sacs, you will definitely have identical twins. Additionally, when your babies share a placenta, there is a greater risk for complications, such as twin-to-twin transfusion syndrome. Your physician will closely monitor your pregnancy to check for potential problems.
   • One placenta and one amniotic sac. This is the riskiest and rarest type of twin pregnancy. Fetal complications can arise due to tangling of the umbilical cords or an imbalance in nutrients, blood or other vital life supporting systems.

2. Do I need to double my caloric intake during a twin pregnancy?

   A common misconception surrounding twin pregnancy is that you need to double your caloric intake to provide your babies with enough nutrients. However, pregnancy nutrition guidelines aren’t simply based on the number of babies you’re carrying. Instead, they’re based on your body mass index at the time you became pregnant.

   Your doctor will make individualized recommendations based on your starting weight. On average, it’s estimated that a woman’s caloric requirements will increase about 40 percent for a twin pregnancy. What’s most important, though, is that a woman eats as healthy as possible.

3. Do I need to take different prenatal vitamins for twins?

   If you’re pregnant with twins, you should take the same prenatal vitamins you would take for any pregnancy, but your physician will recommend extra folic acid and iron. The additional folic acid and extra iron will help ward off iron-deficiency anemia, which is more common when you’re pregnant with multiples.

4. Will I need to visit my doctor more frequently?

   While every pregnancy is different, most women carrying twins will have more frequent prenatal visits than women carrying only one baby. If your twins are sharing one placenta, you will automatically have a more frequent monitoring schedule.

   If your pregnancy doesn’t have complications, your prenatal visits may not differ much from a singleton pregnancy until you get to the end of your second trimester. At that point, you’ll be seen more frequently because there is a higher risk of pre-eclampsia and preterm labor.

5. Do I have to see a maternal-fetal medicine specialist for a twin pregnancy?

   Maternal-fetal medicine specialists see high-risk pregnancies, but not every twin pregnancy will fall into this category.

   To find the best care provider for your twins, make sure that the physician is comfortable managing twins, including vaginal delivery of twins rather than only offering a cesarean section (C-section) for delivery.

6. Are all twin pregnancies delivered preterm?

   A little more than half of twin pregnancies end in preterm delivery (before 37 weeks). While 40 weeks is the full gestation period of the average pregnancy, most twin pregnancies are delivered at approximately 36 weeks (range 32-38 weeks depending on the type of twin pregnancy).

   Unfortunately, preventing preterm labor with multiples is more challenging than with a singleton pregnancy because the interventions used with singleton pregnancies are not as effective with multiples.

7. Can bed rest reduce the risk of preterm delivery?

   Scientific data show that bed rest does not prevent preterm delivery. In fact, bed rest can increase your risk of developing blood clots and have negative financial and social consequences.

   Although bed rest is not prescribed as frequently as it once was, your doctor may suggest reducing your activity level if you’re showing signs of early labor at the end of your second trimester or early in your third trimester.

8. Is labor and delivery significantly different with twins?

   Labor is generally the same whether you’re having one baby or two. During delivery is when things differ significantly.

   When it’s time to deliver your twins, you will go to an operating room even if you are delivering vaginally. This is a safety precaution known as a double setup. Following the vaginal delivery of the first baby, there is a small risk of an emergency cesarean section for the second baby. There is also the possibility of the second twin being delivered breech, which is a safe form of vaginal delivery if the obstetrician is experienced in this type of delivery.

   Of women giving birth to twins over 32 weeks, only about 4 percent who try for a vaginal delivery will have a combined vaginal and cesarean section delivery. While it doesn’t happen very often, by delivering both babies in the operating room, physicians are better prepared to protect the health of the mother and the babies.

   Although being pregnant with twins can seem very different, your doctor will treat your pregnancy like any other unless a complication occurs.

Sign Up for Our Free Newsletter

One of the best things you can do to protect and improve your health is to stay informed. Your Health is a FREE e-newsletter that serves as your smart, simple connection to the world-class expertise of Johns Hopkins.

Sign Up

Related

• Planning a Pregnancy

  How to Prepare for Pregnancy

• Fertility, Pregnancy and Childbirth

  Complications of Pregnancy

• Planning a Pregnancy

  Ovarian Tissue Freezing Cryopreservation

Related Topics

Giving birth to twins | Pregnancy Birth and Baby

Twins are more likely to be born early, often before 38 weeks, so it's important to understand your birth options.  Less than half of all twin pregnancies last beyond 37 weeks.

Because of the likelihood that your babies will be born early, there is a good chance one or both of them will spend some time in special care.

As twins are often born prematurely, it's a good idea to discuss birth options with your midwife or doctor early in your pregnancy.

You should also discuss where you would like to give birth. You will most likely be advised to give birth in a hospital because there's a higher chance of complications with a twin birth.

It's common for more medical staff to be involved in the birth of twins, such as a midwife, an obstetrician and two paediatricians - one for each baby.

While the process of labour is the same as when single babies are born, twin babies are more closely monitored. To do this, an electronic monitor and a scalp clip might be fitted on the first baby once your waters have broken. You will be given a drip in case it is needed later.

Vaginal birth

About one third of all twins are born vaginally and the process is similar to that of giving birth to a single baby. If you're planning a vaginal delivery, it's usually recommended that you have an epidural for pain relief. This is because, if there are problems, it's easier and quicker to assist the delivery when the mother already has good pain relief.

If the first twin is in a head down position (cephalic), it's usual to consider having a vaginal birth. However, there may be other medical reasons why this would not be possible. If you have had a previous caesarean section, it's usually not recommended you have a vaginal birth with twins.

If you have a vaginal birth, you may need an assisted birth, which is when a suction cup (ventouse) or forceps are used to help deliver the babies.

Once the first baby is born, the midwife or doctor will check the position of the second baby by feeling your abdomen and doing a vaginal examination. If the second baby is in a good position, the waters will be broken and this baby should be born soon after the first as the cervix is already fully dilated. If contractions stop after the first birth, hormones will be added to the drip to restart them.

Caesarean section

You may choose to have an elective caesarean from the outset of your pregnancy, or your doctor may recommend a caesarean section later in the pregnancy as a result of potential complications. You’re nearly twice as likely to have a caesarean if you’re giving birth to twins than if you’re giving birth to a single baby.

The babies' position may determine whether they need to be delivered by caesarean section or not. If the presenting baby - the one that will be born first - is in a breech position (feet, knees or buttocks first), or if one twin is lying in a transverse position (with its body lying sideways), you will need to have a caesarean section.

Some conditions also mean you will need a caesarean section; for example if you have placenta praevia (a low-lying placenta) or if your twins share a placenta.

If you have previously had a very difficult delivery with a single baby, you may be advised to have a caesarean section with twins. Even if you plan a vaginal birth, you may end up having an emergency caesarean section.

This could be because:

• one or both babies become distressed
• the umbilical cord prolapses (falls into the birth canal ahead of the baby)
• your blood pressure is going up
• the labour is progressing too slowly
• assisted delivery doesn't work

In very rare cases, you may deliver one twin vaginally and then require a caesarean section to deliver the second twin if it becomes distressed.

After the birth

After the birth, your midwife will examine the placenta to determine what type of twins you have. Twins can either be fraternal or identical.

If your babies need special care

Depending on where you plan to give birth, you may need to go to another hospital with appropriate facilities if complications in your pregnancy indicate you're likely to have an early delivery. This may not be near to home, so make sure to check there are enough beds for both your babies in the neonatal unit.

Ask if your chosen hospital has a transitional care unit or a special care nursery. These are places that allow mothers to care for their babies if they need special care but not intensive care. These hospitals are more likely to be able to keep you and your babies in the same place.

You might also want to ask if your hospital has cots that allow co-bedding (where your babies sleep in a single cot), if this is appropriate and if you want your babies to sleep together.

If you have one baby in the hospital and one at home, you will need to think about splitting your time between the two. When you visit your baby in hospital, ask if you can bring their twin and if co-bedding is allowed during visits.

If you want to breastfeed and only one twin can feed effectively, you may need to express milk to feed the twin who is having trouble feeding. You may then need to put the twin who can feed on the breast to encourage milk production in order to get enough milk to feed both babies.

Check if your hospital offers support from a community neonatal nurse, which would allow for you and your babies to leave hospital earlier, for example if your baby is still tube-fed.

When you go to clinics for follow-up appointments, it's a good idea to ask not to be booked into early morning appointments. Getting out of the house with two babies, particularly if one is unwell, can be difficult.

For more information and support, visit Twins Research Australia.

Learn more here about the development and quality assurance of healthdirect content.

Twin birth - Juno

Twin birth: the content of the article

Twin birth: understanding the terminology

Carrying 2 or more children is a multiple pregnancy. It rarely happens - a maximum of 1.6% of expectant mothers. Now there is an upward trend.

Twins are dizygotic twins. They appear when two eggs fertilize two sperm. Such brothers and sisters are not alike. By appearance, you can determine that they are relatives, but the children are not the same. nine0008

Twins are different and same-sex. They may have a radically different character, temperament.

Causes of twins

Researchers have identified a number of factors that increase the likelihood of conceiving two babies:

• Maturity - in a woman at 35 - 40 years old, the level of gonadotropin increases, it increases the chances of becoming a mother twice in one pregnancy;
• Heredity - women on the line of the future mother had twins. She is also at risk; nine0019
• Genetics - the IGF-1 gene is responsible for tissue development, cell division. There is a direct connection between his rise and the conception of twins;
• High levels of IGF-1 protein - observed in women who are overweight and consume a lot of dairy products. Therefore, vegan women are much less likely to have two babies;
• Hormonal therapy - for example, treatment of infertility with gonadotropins;
• IVF - the procedure involves the stimulation of the ovaries, which leads to the fertilization of two eggs. nine0019
• Nationality - African women most often on the planet give birth to two or more children in one pregnancy.

Scientists from Amsterdam have identified another factor - 2 genes (one or a combination of them). The first is associated with an increase in the FSH hormone, a natural ovarian stimulator for the release of an egg. With a high level of the hormone, 2 eggs can be released.

The second is SMAD3. It is responsible for the reaction of a woman's body to the FSH hormone. If the ovaries are sensitive to it, two eggs can be fertilized. In this case, the level of FSH is not important. nine0008

The first version of the gene increases the chance of carrying and giving birth to two children by 18%, the second - by 9%, their combination - by 29%.

Features of pregnancy

Bearing several fruits is harder than one. After all, the body of the expectant mother works in an increased load mode: the uterus grows, the diaphragm and internal organs are displaced and compressed.

The heart works harder, the urge to urinate becomes more frequent, the woman suffers from shortness of breath and a feeling of lack of air. More weight gain negatively affects the spine, legs, and veins. nine0008

Higher risk of preeclampsia, hemorrhoids, varicose veins, intestinal disorders, heartburn - few pregnant women are lucky to avoid these troubles.

Probability of complications during pregnancy and childbirth of twins

We will determine the risks for the future mother.

Preeclampsia. Diagnosed five times more often. It proceeds more severely, against its background, acute pyelonephritis develops.

Anemia. It develops as a result of iron deficiency - it is consumed in large quantities. nine0008

Gestational diabetes. It occurs more often than when carrying a single child.

pathology of pregnancy. Bleeding, placenta previa, premature birth, miscarriage, abnormalities in labor activity.

Wrong position of children. Low position, breech, foot or mixed presentation complicate the birth of twins.

Postpartum complications. After the first birth (older twin), the uterus may begin to contract - this leads to placental abruption and a threat to the life of a younger brother or sister. nine0008

Massive blood loss. An overstretched uterus can contract poorly after the birth of children. For the mother, this is fraught with blood loss, uterine atony.

Complications for children

Among the risks for babies, doctors point to the following:

• Body weight - less than normal by at least 10%. In most cases, the weight does not reach 2.5 kg;
• Developmental delay. The mother's body is not able to saturate two children at the same time with nutrients and oxygen. Therefore, twins are born small and immature; nine0019
• Unpreparedness for birth. Babies are born prematurely, often severely premature. Even if one baby is ready to meet his mother, then the chances are high that the second one will be less ready for this.

Due dates for multiple pregnancies

In most cases, pregnancy ends at 35-36 weeks.

The birth at 32-33 weeks is assessed as premature. Both or one of the babies may not be ready. The consequences are a lag in physical development, low body weight and height. This is an indication for a caesarean section. nine0008

At 35 weeks, it is advisable for the expectant mother to be hospitalized in the maternity hospital. From now on, a meeting with children can happen at any moment. At 36 weeks, independent childbirth is possible.

The appearance of children at 37 weeks is considered optimal. Usually around this time this happens. They are as ready for the event as possible: healthy, strong. Weigh less than single peers. In the absence of previously identified pathologies, everything proceeds without complications.

At 38 weeks, twins appear extremely rarely. This is the best outcome.

How to calculate the due date of twins

The reference point is the first day of your last period. Subtract 3 months from this day and add 7 days. Here is the expected day of delivery. This method is more suitable for women expecting one child.

It would be more correct for you to subtract 2-3 weeks from this date. If this is your second birth, twins may be born even earlier. nine0008

Duration of twin labor

The birth process includes 3 stages:

• Cervical dilation - from irregular contractions to full dilation;
• Expulsion of the fetus - from attempts to birth;
• Postpartum - from the appearance of the child to the release of the placenta.

The duration of these stages does not depend on the number of fruits. The state of health of their mother plays a role.

The duration of childbirth - the period of exile - is longer than with uniform gestation. This is due to the successive exit of the children. For most women, this step takes 15 minutes. nine0008

The kids go out one after another on average with an interval of 13. 5 minutes.

Method of delivery in multiple pregnancy

Expecting twins is not a reason for operative delivery. With good health of them and their mother, easy bearing and no contraindications, the woman in labor can handle it herself. An important condition is the cephalic presentation of both children, the normal location of the placenta.

In case of complications, pathology of pregnancy, contraindications on the part of the mother or babies, surgical intervention is indicated. nine0008

Natural childbirth

First, the harbingers of an imminent meeting with babies come.

The stomach drops - mom breathes easier. With repeated births, the stomach drops shortly before an important event - in a couple of days, with a third it may not fall.

Liquid stool is the second harbinger. Substances are more actively released to start the contractile activity of the uterus. They also irritate the intestines.

Increased urge to the toilet "in a small way. " The uterus presses on the bladder - urination becomes more frequent. nine0008

Decreased activity in children. The symptom is not typical for everyone.

Pain. The sacrum, lower back aches - twins can appear from day to day or even in the next few hours.

In first-born mothers, these signs are more pronounced.

The beginning of the birth process

It starts with contractions - this is how the uterus opens. They are accompanied by severe pain, regular and growing.

The birth process proceeds according to the standard scheme. Some stages are specific. nine0008

The sequence is:

• Neck fully open;
• The eldest child is born: the waters break from the bladder, and the child is born;
• Pause;
• The youngest child is born. By the same principle;
• Sequence out.

If the water does not leave, the fetal bladders are pierced - an amniotomy is performed.

Delivery of twins by caesarean section

In some maternity hospitals, patients are given the opportunity to choose the method of delivery. If there are strict indications for surgery, it is carried out as planned at 38 weeks. A planned intervention allows you to avoid risks and complications, preserve the health and life of mothers and children.

Mom’s indications are health problems: HIV, a scar on the uterus, genital herpes, disruption of the heart and blood vessels, neoplasms in the genitourinary area, poor eyesight, cervical spasm. nine0008

Indications on the part of children - pregnancy pathologies: hypoxia, transverse position, breech or different presentation, low placentation. In breech presentation, the weight of the child is taken into account: less than 0.5 or more than 3.5 kg is an indication for caesarean section.

There is a risk of an emergency caesarean section. For example, with weak labor activity, stimulation is not carried out with twins, but is immediately taken to the operating room.

Twin birth: natural or caesarean section

PreviousNext

Contents:

1. Why do multiple pregnancies and twin births happen?
   • Fraternal twins
   • Identical twins
   • Features of pregnancy by identical twins depending on the time of separation of the zygote.
2. Can a woman have twins in her first birth?
3. How often do twin births occur? nine0019
4. How long does a twin birth take?
5. When is the due date for multiple pregnancies?
6. Which is better for twins - caesarean section or natural childbirth?

The human reproductive system is very economical, and usually a woman becomes the mother of one baby. However, occasionally we come across parents walking with a double stroller or trying to fit two identical toddlers into a car. Why it happens? What is the probability of becoming a mother of twins? What awaits a woman when the time comes for twins to be born - caesarean section or natural childbirth? We answer your questions. nine0008

Why do multiple pregnancies and twin births happen?

Sometimes two or even more babies begin to grow in the womb of a future mother at once. If you do not consider unique and very rare cases, then twins can be homozygous (identical, emerging from the same egg) and heterozygous (fraternal, grown from different eggs).

Fraternal twins

Heterozygous twins appear when several eggs mature in a woman at the same time. Babies are always isolated - each of them has an individual placenta and fetal (amniotic) bladder. They may have different sexes, and, in general, they usually resemble each other no more than the children of this couple, born several years apart from different pregnancies. At the same time, eggs can be fertilized both as a result of one sexual intercourse, and different - with an interval of several hours or days. nine0008

If a woman has a very active sex life, it is even possible that one egg is fertilized by the sperm of one partner, and the second by the other. Then, during the birth of twins, babies are born, each of which has its own father, which in scientific language is called the term "superfecundation". The exact frequency of this phenomenon is unknown, but in cases where DNA examinations were performed when paternity was disputed (in other words, when potential dads suspected in advance that the matter was unclean), superfecundation was confirmed in 2.4% of twin pairs ¹ .

The birth of several babies is not an ordinary situation. The expectant mother of twins needs to carefully monitor her health and try to understand all the intricacies of pregnancy in more detail. These materials will help:

• How to conceive twins?

• How is a multiple pregnancy?

• What can and cannot be eaten during pregnancy? nine0008

Identical twins

Monozygotic twins are a different story. At first, everything happens as usual: one egg comes out of the follicle during ovulation, it is fertilized by one sperm, it becomes one zygote (a cell with the combined genetic material of the parents), from which one embryo should develop. But after a while, it suddenly splits into two identical copies. One of them can divide again, and then instead of giving birth to twins, the mother will give birth to triplets, if both zygotes do this, there will be four twins. nine0008

Features of pregnancy by identical twins depending on the time of separation of the zygote.

If fraternal twins always have separate "apartments" - each has its own placenta and amniotic bladder, in identical twins it depends on the time of separation ² .

60–70%

Can a woman have twins in her first birth?

Everything is possible. Do you remember that multiple pregnancies can be identical and heterozygous? The likelihood of developing identical twins is the same for all women. In both first and subsequent births, twins of identical babies are born in about 4 out of 1000 pregnancies ³ .

Fraternal twins appear for a different reason - due to hyperovulation, i.e. maturation of two or more eggs in one cycle. This is influenced by the following factors ⁴ :

• Use of fertility drugs.

• Recent withdrawal of hormonal contraceptives or irregular use of contraceptives.

• Obesity, i.e. body mass index above 305.

• Genetic predisposition. If you yourself have a twin, if your mother or your sister gave birth to twins, your chances are higher than the average natural probability of giving birth to twins ⁶ .

• Rost. Tall women are more likely to become mothers of fraternal twins.

• Woman's age. The likelihood of multiple pregnancy increases after age 35 ⁷ . nine0008

How often do twins occur?

In obstetrics, there is the so-called Hellin's law ⁸ , which states that the probability of having twins, triplets, etc. obeys the following formula: 1/89N-1, where N is the number of twins.

Number of fruits	Probability	nine0007 Percentage
2	1 out of 89 births	1.1%
3	1 out of 7921 births	nine0007 0. 013%
4	1 out of more than 700 thousand births	0.00014%

Hellin's law is just a curious observation made by a late 19th century physician, and modern science offers much more complex formulas. However, sometimes it works amazingly. For example, in 2016 in Russia there were 1,876,646 births, in which 22,144 twins and 408 triplets were born ⁹ , which in percentage terms is 1.18% and 0.021%. Not bad accuracy!

In general, the statistics of twin births in our country looks like this:

Percentage of twin births among all births in Russia from 1996 to 2016 ⁹ .

It is easy to see that in the late 1990s and early 2000s, the statistics were almost constant, and then unexpectedly but surely crept up. The answer is simple: medicinal and other assisted reproductive technologies have been actively developing lately, and they often lead to multiple pregnancies ¹⁰ . So the last numbers are naturally occurring twins plus the contribution of infertility treatments.

How long does it take to give birth to twins?

Doctors distinguish three stages in childbirth - the period of disclosure, the period of exile and the subsequent period. The first period begins with contractions and ends with the full opening of the cervix, the third starts after the birth of the baby and ends with the appearance of the afterbirth - the placenta and the remains of the membranes. The duration of these periods depends more on the individual characteristics of the body than on how many babies the woman bore. nine0008

Of greatest interest is the period of exile - the very one when babies from a cozy mother's womb are "expelled" into our difficult world. They come out sequentially, which means that we can assume that the birth of twins is longer for this particular interval between the appearance of the first and second child. So how much does he make?

Thanks to doctors from the Hesse region in Germany, this question has a very precise answer. For 15 years, they carefully researched information about natural births of twins in local hospitals. As a result, an impressive amount of data was collected - more than 4,000 cases of multiple pregnancies, as a result of which more than 8,000 babies were born. The analysis of this array made it possible to calculate the most probable interval that passes between the birth of babies in twin births in a natural way. For 3 out of 4 mothers, this takes no more than 15 minutes, and on average, one twin is only 13.5 minutes older than the other ¹¹ .

16.4%

Occasionally, in obstetric practice, surprising cases are noted when a much longer time passes between the birth of twins. Apparently, the first position among the record holders for the duration of the birth of twins is occupied by a resident of the German city of Cologne named Oksana (we will not say, but the name suggests that she may be our former compatriot).

On November 17, 2018, at the 26th week of pregnancy, a woman went into premature labor. She gave birth to a live premature baby girl weighing 900 grams, after which the cervix closed and the contractions stopped. The doctors decided to give the second child the opportunity to stay in the mother's womb as long as possible. As a result, another girl was born four days after the planned date - 97 days later than her sister and already in 2019 ¹² . By the way, don't worry about the older baby: the doctors took her out, and after a three-month separation, the twins met again.

When is the due date for multiple pregnancies?

A woman who has several children has a significantly higher chance of becoming a mother ahead of schedule. Doctors will try to do everything to prolong the pregnancy as much as possible, but the woman herself should not risk the future of her babies either. At the very least, she needs to monitor her diet and health, breathe fresh air, avoid psychological stress and excessive physical exertion. nine0008

Useful services for expectant mothers:

• Are you ready to be a super mom? This test will show

• What do you need to take to the hospital? Here is the complete list of

• Free video courses for moms from pediatricians at Huggies Parents School

Which is better for twins - caesarean section or vaginal delivery?

The final decision on the tactics of childbirth is made by the specialists of the maternity hospital, guided by all the information available to them about the pregnancy. However, practice shows that if everything goes on the whole normally (the gestational age at the time of delivery exceeds 32 weeks, and the first twin is settled in head presentation, that is, it is going to go head first), there is no significant difference between the natural birth of twins and caesarean section ¹⁴ . A large study involving 106 medical centers in 25 countries showed that the risk to babies remains the same with both modes of delivery.

Cesarean section is indicated for breech presentation of the first twin in twin birth. However, in this situation, the operation is recommended even during pregnancy with one baby. If the twins are growing up in a common amniotic sac, doctors also usually opt for a caesarean section. In other cases, you should not be afraid of giving birth to twins in a natural way - they are no more dangerous than surgery ¹⁴ .

Sources:

1. Wenk, R. E.; Houtz, T; Brooks, M; Chiafari, F. A. (1992). How frequent is heteropaternal superfecundation? Acta geneticae medicae et gemellologiae. 41(1):43–7.

2. Curran, Mark (2005-11-02). twinning. Focus Information Technology.

3. Professor Hanan Hamamy. GFMER. Monozygotic twinning.

4. nine0007 Joel Forman, MD. Causes of Identical and Fraternal Twins.

5. WebMD. Moms' Obesity Makes Twins More Likely.

6. U.S. National Library of Medicine. Is the probability of having twins determined by genetics?

7. ACOG. Multiple Pregnancy.

8. Johan Fellman (November 5th 2018). Historical Studies of Hellin's Law, Multiple Pregnancy - New Challenges, Julio Elito Jr., IntechOpen. nine0008

9. Federal State Statistics Service (Rosstat). Demographic Yearbook of Russia. 2017: Stat. Sat / Rosstat. - M., 2017. - 263 p. ISBN 978-5-89476-447-4.

10. Kulkarni AD, Jamieson DJ, Jones HW, Kissin DM, Gallo MF, Macaluso M, Adashi EY (2013). Fertility Treatments and Multiple Births in the United States. New England Journal of Medicine. 369(23): 2218–2225.

11. Stein W, Misselwitz B, Schmidt S (2008). "Twin-to-twin delivery time interval: influencing factors and effect on short-term outcome of the second twin". Acta Obstet Gynecol Scand. 87(3): 346–53. nine0008

12. Twins born three months apart in different YEARS hailed 'medical sensation'.

13. Nanette Elster (J.D., M.P.H.). Institute for Science Law and Technology Working Group on Reproductive Technology. Less is more: the risks of multiple births.

14. Barrett JF, Hannah ME, Hutton EK, Willan AR, Allen AC, Armson BA, Gafni A, Joseph KS, Mason D, Ohlsson A, Ross S, Sanchez JJ, Asztalos EV (2013).

    ---

    Learn more

    • 
      How to raise a scorpio child
    • 
      When to worry about morning sickness
    • 
      Partial molar pregnancy pictures
    • 
      Twenty five weeks pregnancy
    • 
      What to expect in your third trimester
    • 
      Early signs of pregnancy hungry
    • 
      What do miscarriages look like at 6 weeks
    • 
      Sunburn that turns into a rash
    • 
      Baby delivery position
    • 
      Twenty five weeks pregnancy
    • 
      What to expect in your third trimester