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How is pregnancy dated


Baby due date - Better Health Channel

Summary

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  • The unborn baby spends around 38 weeks in the uterus, but the average length of pregnancy, or gestation, is counted at 40 weeks.
  • Pregnancy is counted from the first day of the woman’s last period, not the date of conception which generally occurs 2 weeks later.
  • Since some women are unsure of the date of their last menstruation (perhaps due to period irregularities), a baby is considered full term if its birth falls between 37 to 42 weeks of the estimated last menstruation date.

The unborn baby spends around 37 weeks in the uterus (womb), but the average length of pregnancy, or gestation, is calculated as 40 weeks. This is because pregnancy is counted from the first day of the woman’s last period, not the date of conception which generally occurs 2 weeks later, followed by 5 to 7 days before it settles in the uterus.

Since some women are unsure of the date of their last menstruation (perhaps due to period irregularities), a pregnancy is considered full term if birth falls between 37 to 42 weeks of the estimated last menstruation date.

A baby born prior to week 37 is considered premature, while a baby that still hasn’t been born by week 42 is said to be overdue. In many cases, labour will be induced in the case of an overdue baby.

The average length of human gestation is 280 days, or 40 weeks, from the first day of the woman’s last menstrual period. The medical term for the due date is estimated date of confinement (EDC). However, only about 4 per cent of women actually give birth on their EDC.

There are many online pregnancy calculators (see Baby due date calculator) that can tell you when your baby is due, if you type in the date of the first day of your last period.

A simple method to calculate the due date is to add 7 days to the date of the first day of your last period, then add 9 months. For example, if the first day of your last period was 1 February, add 7 days (8 February) then add 9 months, for a due date of 8 November.

Determining baby due date

Irregular menstrual cycles can mean that some women aren’t sure of when they conceived. Some clues to the length of gestation include:

  • Ultrasound examination (especially when performed between 6 and 12 weeks)
  • Size of uterus on vaginal or abdominal examination
  • The time fetal movements are first felt (an approximate guide only).

Pregnancy ultrasound

A pregnancy ultrasound is a non-invasive test that scans the unborn baby and the mother’s reproductive organs using high frequency sound waves.

The general procedure for a pregnancy ultrasound includes:

  • The patient lies on a table.
  • A small amount of a clear, conductive jelly is smeared on the abdomen.
  • The operator places the small hand-held instrument called a transducer onto the abdomen.
  • The transducer is moved across the abdomen. The sound waves bounce off internal structures (including the baby) and are transmitted back to the transducer. The sound waves are then translated into a two-dimensional picture on a monitor. The mother will not feel or hear the transmission of the sound waves.
  • By measuring the baby’s body parts, such as head circumference and the length of long bones, the operator can estimate its gestational age.

The diagnostic uses of pregnancy ultrasound

Apart from helping to pinpoint the unborn baby’s due date, pregnancy ultrasounds are used to diagnose a number of conditions including:

  • multiple fetuses
  • health problems with the baby
  • ectopic pregnancy (the embryo lodges in the fallopian tube instead of the uterus)
  • Abnormalities of the placenta such as placenta previa, where the placenta is positioned over the neck of the womb (cervix)
  • The health of the mother’s reproductive organs.

Premature babies

A baby born prior to week 37 is considered premature. The odds of survival depend on the baby’s degree of prematurity. The closer to term (estimated date of confinement, or EDC) the baby is born, the higher its chances of survival – after 34 weeks gestation with good paediatric care almost all babies will survive.

Premature babies are often afflicted by various health problems, caused by immature internal organs. Respiratory difficulties and an increased susceptibility to infection are common.

Often there is no known cause for a premature labour; however, some of the maternal risk factors may include:

  • drinking alcohol or smoking during pregnancy
  • low body weight prior to pregnancy
  • inadequate weight gain during pregnancy
  • no prenatal care
  • emotional stress
  • placenta problems such as placenta previa
  • various diseases such as diabetes and congestive heart failure
  • infections such as syphilis.

Overdue babies

Around 5 out of every 100 babies will be overdue, or more than 42 weeks gestation. If you have gone one week past your due date without any signs of impending labour, your doctor will want to closely monitor your condition.

Tests include:

  • monitoring the fetal heart rate
  • using a cardiotocograph machine
  • performing ultrasound scans.

The placenta starts to deteriorate after 38 weeks or so, which means an overdue baby may not get enough oxygen. An overdue baby could also grow too large for vaginal delivery. Generally, an overdue baby will be induced once it is 2 weeks past its expected date.

Some of the methods of induction include:

  • Vaginal prostaglandin gel - to help dilate the cervix.
  • Amniotomy – breaking the waters, sometimes called an artificial rupture of membranes (ARM).
  • Oxytocin – a synthetic form of this hormone is given intravenously to stimulate uterine contractions.

Where to get help

  • Your GP (doctor)
  • Obstetrician
  • Midwife
  • Your local maternal and child health service

  • Common concerns and discomforts: overdue baby, Mother’s Bliss, UK.
  • Going Overdue, Centre for Reproduction and Minimally Invasive Surgery.
  • Premmie-L FAQ and advice sheets, Parents of Premature Babies Inc.(Preemie-L).
  • Pregnancy: what to expect when it’s past your due date, Family Doctor, USA.
  • Ultrasound, The Royal Women’s Hospital, Melbourne.

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How are Due Dates Calculated

Keywords

Dani Kurtz

If you were having regular periods before pregnancy, your doctor will calculate your due date based off of your last menstrual period. This goes back to the fact that in order to get pregnant, your body ovulated—or released an egg—roughly in the middle of your cycle and it was fertilized by sperm. That was the moment of conception.

By the time most women miss a period and find out they’re pregnant, the baby has been growing for 2 weeks, but the mother is actually 4 weeks along because the gestational period starts with the first day of your last period.

To clarify, the gestational period of 40 weeks actually starts with the first day of your last period, which adds two weeks of time to the gestational period when your baby didn’t even exist yet…clear as mud, right?

Is an ultrasound a more accurate way of finding out my due date?

If you are having irregular cycles before getting pregnant, an ultrasound is usually done to find out how far along you are. An ultrasound is actually the most accurate way to date a pregnancy because all fetuses grow at a consistent rate during the first trimester and early second.

In other words, if your baby measures 9 weeks 2 days when you have your ultrasound, that’s how far along you are, no matter when your last period was.

Some women with regular cycles are confused about why their ultrasound due date doesn’t match up with their last menstrual period due date. Ovulation isn’t a perfect science and can happen earlier or later than the norm, which might shift your due date slightly.

That’s okay…a few days or even a week of discrepancy won’t change your dates. Your doctor will go with the due date obtained from your ultrasound.

What happens if my baby is measuring big or small later on? Does my due date need to change or will I deliver early?

You’ll notice at every prenatal appointment after 20 weeks, your doctor will measure your belly. That measurement should match your gestational age in centimeters. If you are measuring smaller or larger than what you should be, then the doctor might order an ultrasound. This will tell them if the discrepancy is due to the actual size of the baby, the amount of fluid surrounding the baby, or maybe just the way you’re carrying the baby.

If the baby is actually smaller or larger than what they should be, underlying issues need to be considered that might be causing the discrepancy in growth. For example, mothers with uncontrolled diabetes (Type 1, Type 2, or Gestational) cook very large babies. When a baby is small, it might be due to a placenta that’s not working like it should.

These discrepancies might affect delivery, but they might not. For example, if your baby is consistently measuring small and falling below where they should be, your doctor might decide you need to be delivered because your baby would be better out than in.

If your baby is extra big and you’re measuring 40 weeks at 37 weeks, your body might think it’s done and go into labor early….or you might go to your due date and things will go as planned. If you have questions about your due date, talk with your doctor who can give you the best information.

Intermountain Moms

Last Updated: 10/27/2017

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Pregnancy causes long-term changes in the structure of the brain

A team of researchers from Spain and Holland showed that pregnancy causes changes in the structure of the gray matter of the brain that persist for at least two years after birth. The article was published in the journal Nature Neuroscience , its content is briefly described in the editorial material of the journal Science .

During pregnancy, the level of sex steroid hormones varies greatly: for example, the amount of estrogens produced during pregnancy usually exceeds the total amount of estrogens produced in the woman's body for all other periods of her life. At the same time, previous studies have shown that changes in the level of sex steroid hormones can cause structural and functional changes in the nervous tissue of the brain. For example, during puberty, the production of sex hormones causes a massive reorganization of the brain, and in adults, a change in the level of steroid sex hormones leads to neural restructuring. It is not surprising, therefore, that in rodents and other animals, studies have shown that pregnancy causes changes in the nervous tissue at several levels at once, including changes in the morphology of dendrites, the intensity of neuronal division and gene expression. In humans, however, there have been few systematic studies of this kind. It is only known that in the later stages of pregnancy, the size of the pituitary gland increases and the total volume of the brain decreases. nine0007

The authors of a new article used magnetic resonance imaging to trace changes in the structure of the gray matter of the brain in 25 women who were pregnant for the first time in their lives. Their brains were scanned before pregnancy and after childbirth (after different periods of time: from three weeks to several months). Also included in the analysis were 20 nulliparous non-pregnant women and, to exclude the influence of parenthood (and not specifically pregnancy), 19 men who became fathers for the first time, and 17 men who did not have children. For all these groups, brain scans were performed at the same time intervals as for the test group of pregnant women. nine0007

It turned out that all women who had given birth had very similar changes in gray matter volume of the brain - so similar that all women participating in the study could easily be classified into parous and nulliparous solely on the results of their brain scans. Most of the changes were concentrated in the areas of the brain responsible for social skills - such as understanding the emotions and intentions of other people from their faces and actions. The hippocampus, an area of ​​the brain that plays a key role in memory formation, also decreased in volume. No such changes were observed in any of the control groups. However, a decrease in the volume of the hippocampus did not affect the memory of women who gave birth: they coped with memory tasks no worse than before pregnancy. The only thing that the researchers managed to notice was a slight deterioration in verbal memory (however, the level of differences was not statistically significant). nine0007

By measuring the strength of women's attachment to their children using a standard test, the researchers also found that the strength of attachment correlated with how much a woman's brain changed during pregnancy: the greater the change, the stronger the attachment. The scientists also looked at how women's brains react to photos of their own children and photos of other people's children (how different the brain's response to these stimuli is also a measure of the strength of attachment). It turned out that about 30 percent of those areas of the brain that are selectively activated in response to photographs of their own (rather than other people's) children coincide with the areas of the brain that changed volume during pregnancy. nine0007

Two years after these studies, 11 out of 25 mothers - those who did not become pregnant again during this time - again underwent magnetic resonance imaging of the brain. It turned out that these women still have a reduced volume of gray matter in the same areas of the brain - with the exception of the hippocampus, the volume of which returned to its original state. The surviving changes were also sufficient to determine on their basis alone whether a woman was pregnant in the past or not.

What exactly is the reason for the decrease in the volume of gray matter - with a change in the number of synapses or neurons, with a restructuring of the dendritic structure, or with a change in the blood supply to the brain - is still unclear. As the authors note, the decrease in gray matter volume observed during puberty is associated (at least in part) with the so-called synaptic pruning: a reduction in the number of synapses to remove redundant connections and increase the efficiency of neural networks. It is possible that similar processes occur during pregnancy, increasing the efficiency and specialization of the work of individual parts of the brain. In some studies, for example, it has been shown that pregnant women have an improved ability to recognize faces and emotions. The authors suggest that this may be due to the changes in the brain regions responsible for social skills that they observed in their study. nine0007

Sofia Dolotovskaya

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Ultrasound during pregnancy. Features, description of the method

Main Articles Ultrasound during pregnancy. Features, description of method

Prenatal ultrasound is a non-invasive diagnostic test that uses sound waves to create a visual image of the fetus, placenta, uterus, and other pelvic organs of a pregnant woman. Allows the doctor to obtain valuable information about the course of pregnancy and the health of the baby. During the procedure, an ultrasound machine or scanner transmits high-frequency sound waves. They pass through the uterus, are reflected from the baby. The computer captures the information received, translates it into a video image format that shows the shape, position and movements of the child. Rigid tissues, such as bones, appear white in the image, as they reflect a large number of sound waves. Soft tissues appear grey. The fluids surrounding the fetus appear black on the screen because the sound waves simply pass through them and are not reflected. nine0007

Timing of the procedure

The pregnancy doctor determines when a fetal ultrasound is required.

  • As a rule, the first ultrasound is prescribed at 10-14 weeks of pregnancy. The purpose of the first scan is to check how many children a woman is carrying, whether they are developing normally. The procedure during the first trimester provides information about the basic anatomy of the head, abdominal wall, limbs, and checks whether the baby's heart is beating. The first ultrasound examination gives parents and the doctor a first impression of the baby. The resulting image can be printed and saved as a keepsake. nine0038
  • 19-23 weeks. The size, gender of the fetus is revealed. There is an assessment of the growth rate of the child, the development of internal organs. The presence or absence of chromosomal abnormalities can already be said at this stage.
  • 32-36 weeks. It is carried out for the purpose of diagnosing late anomalies. The date of birth is specified.

Purpose

Depending on the stage of pregnancy, an ultrasound examination is used to obtain the following information:

  • Check that the baby's heart is beating
  • Determine if a woman is pregnant with one child, twins or more
  • Detect ectopic pregnancy (when the embryo begins to develop outside the uterus)
  • Find cause of bleeding if present
  • Accurately date pregnancy by measuring baby
  • Assess the risk of having a baby with Down syndrome by measuring the fluid in the back of the neck of an embryo at 11-14 weeks of gestation
    • nine0037 Determine the cause of abnormal blood tests
  • Assess the position of the baby, placenta, amount of amniotic fluid
  • Examine the child, make sure that the organs are normal
  • Diagnose violations
  • Measure the child's growth rate based on previous scans.
  • Determination of the sex of the child. In some cases, the child assumes an awkward position, and it is difficult to say a boy or a girl.
    • nine0043

    Procedure

    No special training required. Your doctor may ask you to drink several glasses of water to keep your bladder full. This will help the specialist see the child better. The patient lies on his back on a chair. A special gel is applied to the abdomen to improve the conduction of sound. The doctor slowly moves a small transducer across the abdomen. The video image is displayed on the monitor.

    Basic Scan takes 15 to 20 minutes. A more detailed study is carried out using more sophisticated equipment within 30-90 minutes. When carrying out the procedure in early pregnancy, a vaginal scan is prescribed. Prenatal ultrasound is a painless procedure that does not cause discomfort.

    3-D and 4-D scanning

    New technologies make it possible to obtain a three-dimensional image of the fetus. In terms of clarity and clarity, the result is similar to a photograph. The procedure may be helpful in detecting birth defects in the fetus.

    Norm of indication