Days from conception to birth

Baby due date - Better Health Channel

Summary

Read the full fact sheet

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 two 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 two weeks later, followed by five to seven 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 four 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 seven days to the date of the first day of your last period, then add nine months. For example, if the first day of your last period was 1 February, add seven days (8 February) then add nine 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 six 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 woman lies on a table.
A small amount of a clear, conductive jelly is smeared on the woman’s abdomen.
The operator places the small hand-held instrument called a transducer onto the woman’s 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 doesn’t 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 praevia, 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 praevia
Various diseases such as diabetes and congestive heart failure
Infections such as syphilis.

Overdue babies

Around five 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 two 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 doctor
Your obstetrician
Midwife or childbirth educator

Things to remember

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 two 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 its estimated due date.

Common concerns and discomforts: overdue baby, Mother’s Bliss, UK.
Going Overdue, 2001, Centre for Reproduction and Minimally Invasive Surgery.
Premmie-L FAQ and advice sheets, Parents of Premature Babies Inc.(Preemie-L). More information here.
Pregnancy: what to expect when it’s past your due date, Family Doctor, USA.
Ultrasound, Women Health Information, Royal Women’s Hospital, Melbourne. More information here.

This page has been produced in consultation with and approved by:

Baby due date - Better Health Channel

Summary

Read the full fact sheet

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 two 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.

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 six and 12 weeks)
Size of uterus on vaginal or abdominal examination
The time fetal movements are first felt (an approximate guide only).

Pregnancy ultrasound

The woman lies on a table.
A small amount of a clear, conductive jelly is smeared on the woman’s abdomen.
The operator places the small hand-held instrument called a transducer onto the woman’s 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 doesn’t 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 praevia, where the placenta is positioned over the neck of the womb (cervix)
The health of the mother’s reproductive organs.

Premature babies

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 praevia
Various diseases such as diabetes and congestive heart failure
Infections such as syphilis.

Overdue babies

Monitoring the fetal heart rate
Using a cardiotocograph machine
Performing ultrasound scans.

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 doctor
Your obstetrician
Midwife or childbirth educator

Things to remember

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 two 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 its estimated due date.

Common concerns and discomforts: overdue baby, Mother’s Bliss, UK.
Going Overdue, 2001, Centre for Reproduction and Minimally Invasive Surgery.
Premmie-L FAQ and advice sheets, Parents of Premature Babies Inc.(Preemie-L). More information here.
Pregnancy: what to expect when it’s past your due date, Family Doctor, USA.
Ultrasound, Women Health Information, Royal Women’s Hospital, Melbourne. More information here.

This page has been produced in consultation with and approved by:

How to correctly calculate the gestational age and determine the date of delivery

It often comes as a surprise to first-time pregnant women that in obstetrics the gestational age is determined not in months, but in weeks. But the surprises do not end there - the fact is that the obstetric period is calculated not from conception, but from the first day of the last menstruation.

In fact, pregnancy occurs two weeks after the start of the obstetric period, at the time of ovulation, when the sperm meets the egg. Thus, the age of the embryo, or gestational age, differs from the obstetric one by 2 weeks down.

How long does pregnancy last?

The obstetric term of a term pregnancy is 40 weeks, or 280 days. It is on the basis of the obstetric gestational age that the doctor will prescribe tests and examinations for you, determine the date of maternity leave and calculate the EDD (estimated date of birth).

Doctors use the Negele formula to calculate the EDD. According to this formula, if we add nine months and seven days to the first day of the last menstruation, we get the estimated date of delivery.

Unfortunately, determining the gestational age from the first day of the last menstrual period is not a very accurate method. It is well suited for women with a stable 28-day cycle, but if your cycle is slightly longer or shorter, then the date of ovulation shifts, respectively, and the actual obstetric gestational age will differ from the established one.

The most accurate way to calculate the EDD is to add 266 days to the date of the last ovulation (if you know it).

How to confirm pregnancy, determine the duration of pregnancy and the date of delivery

By itself, a delay in the start of a new menstrual cycle does not necessarily indicate pregnancy - failures can be explained by diseases, excessive physical exertion or stress. Pregnancy must be confirmed with an hCG test or examination on a gynecological chair. 1) Blood test for hCG cycle or the woman will feel the first symptoms. Also, an analysis of the level of hCG in the blood allows you to determine the gestational age with an accuracy of about two weeks.

2) Home pregnancy test

Home pregnancy tests also work by measuring hCG levels, but they are less sensitive than blood tests. The most modern of them can not only confirm the presence of pregnancy a few days before the delay, but also indicate (not too accurately) an approximate date.

Tests of the old generation will show a more or less accurate result only after a delay, that is, after 2-4 weeks from conception.

3) Gynecological examination

A qualified gynecologist-obstetrician can diagnose pregnancy during an examination starting 3-4 weeks after conception, focusing on changes in the shape and size of the uterus, as well as other signs.

4) Ultrasound

Ultrasound is the most accurate way to diagnose pregnancy. With the help of ultrasound with a transvaginal sensor, it is possible to determine the presence of a fetal egg in the uterus already 1-2 weeks after conception (3-4 obstetric weeks), but fetal heartbeats can only be detected for a period of 5-6 obstetric weeks. It is possible to determine the gestational age with high accuracy (up to 2-3 days!) With the help of ultrasound only from 6-7 weeks.

If the delay, as well as the result of an hCG test or blood test, indicate that you will soon become a mother, do not rush to get an ultrasound right away. Wait another 2-3 weeks, then by ultrasound you will not only be accurately determined by the period, but will also be allowed to listen to the baby's heartbeat.

If you did not do an early ultrasound to confirm pregnancy, then for the first time you will encounter this study at the 10-14th week. At the same time, the exact gestational age and PDR will be established or corrected for you. During pregnancy, you will need to undergo such an examination at least twice more. This will happen at 20-24 and 30-34 weeks. However, it is worth saying that ultrasound in the 2nd and 3rd trimesters may have an error in determining the gestational age. The PDR established according to them may differ from the real one by 2-3 weeks. That is why it is so important not to miss the first screening and do an ultrasound on time.

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Normal pregnancy in women can vary within five weeks

August 08, 2013, 10:28 Science

100%

Scientists questioned the seemingly unshakable fact that a child develops in the womb for nine months. They just accurately calculated the timing and received a lot of interesting information.

The duration of pregnancy in a woman - it would seem, what could be new here? Of course, the well-known nine months is very rounded. Doctors calculate the expected date of birth of a child by counting 280 days from the start of the last menstrual period.

But, according to statistics, only 4% of women give birth after the prescribed 280 days, and 70% fit within plus or minus ten days from the appointed date.

An unexpected conclusion was reached by specialists of the National Institute for Health and the Environment in Durham, USA. They have shown that the length of a normal pregnancy can vary over a wide range of 37 days, and reported their findings in Human Reproduction .

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The timing of such important processes as ovulation (release of a mature egg from the ovary) and implantation of the embryo into the uterus has so far been estimated very roughly. So, doctors determine the moment of ovulation by raising the morning rectal temperature. But this method carries a large error and, moreover, does not say anything about when the embryo was introduced into the uterine mucosa.

The essence of the approach used in this study is the accuracy of determining the moment of conception.

The team used information from 130 women who had previously participated in the North Carolina Pregnancy Study. During the study, urine samples were collected daily from women, which were examined for hormone levels. Changed hCG (chorionic gonadotropin), estrone-3-glucuronide and pregnanediol-3-glucuronide. The day of ovulation was determined by the fall in the ratio between estrogen and progesterone. And the moment of implantation of the embryo into the uterus was defined as the first day of the rise in the level of hCG.

Specialists analyzed the timing of delivery in 125 women with normal pregnancies. And it turned out that the time from the moment of conception to the moment of the birth of a child varies quite a lot.

"We calculated that the average time from ovulation to delivery is 268 days - 38 weeks and two days," says Anna Maria Jukis, study author. “However, even when we excluded six cases of preterm birth, we found that the duration of pregnancy varied within 37 days.”

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Until now, it was thought that the variation in the duration of pregnancy was due to errors in determining its onset. Scientists have eliminated errors - and the scatter has even increased. "It's amazing!" Jukis says.

In addition to the variability in the duration of pregnancy, scientists have found that the embryo, which takes longer to implant in the uterus after fertilization of the egg, develops longer. And if at the beginning of pregnancy there was a late rise in progesterone, the pregnancy was shorter than with an early rise, on average by 12 days. Experts were surprised by the fact that the events that occur at the very beginning of pregnancy have an impact on its outcome - on the time of the birth of the child. They conclude that by observing the onset of pregnancy, it is possible to some extent predict its end.

Jukis and colleagues analyzed a variety of factors that showed a correlation with the duration of pregnancy.

Older women had longer pregnancies, with each year of a woman's age adding one day to her pregnancy.

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And women who themselves had more weight at birth, bore their child longer. Experts calculated that for every 100 grams of birth weight a mother added one day to her pregnancy. Finally, if a woman's previous pregnancies lasted longer than the average, then the subsequent pregnancy was longer. The latter is regarded by experts as evidence of the influence of a woman's individuality on this indicator.

So, the authors of the study come to the conclusion that the duration of a woman's pregnancy can vary greatly and depends on many factors, even with an accurate determination of the moment of ovulation. They suggest that the "timecode" of pregnancy can be more or less accurately determined based on the hormonal events of the first two weeks after conception and the length of previous pregnancies.

However, they believe that it is premature to make any clinical recommendations based on the results obtained. This will require additional research. But at the very least, doctors need to be aware that five weeks off the estimated due date is normal.

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