9 months, the number everyone remembers when it comes to the length of pregnancy. But what is it really? And does it really hold true? Here is everything there is to know about the term of pregnancy and how to calculate the onset and due date. Keep in mind, however, that there is no such thing as a 100% reliable way, but that doesn't mean you should worry.
From one woman to another, the duration of pregnancy will vary, depending on many factors, such as age, genetics, sometimes weight but also on previous pregnancies if it is not the first child. Despite everything, we generally assume that the gestation period is around 280 days, or 40 weeks, but a delivery from the 37th week is considered to be at term, without risk for the baby.
SA, SG, LCC: three methods to calculate the onset and term of pregnancy
There are several ways to determine, with varying degrees of precision, the date of onset of pregnancy, that is, conception, and thus the term and expected date of delivery (dpa). The two most common, which are weeks of amenorrhea (SA) and weeks of pregnancy (SG), are based on the menstrual cycle of the expectant mother but do not take into account the same starting point.
Pregnancy weeks (SG)
The onset of pregnancy occurs when an egg is fertilized by a sperm. However, ovulation usually occurs at 14 days of a 28-day cycle. This will be considered the day of conception and will count for 39 weeks. For example, if your last period was on June 10, the onset of pregnancy would be considered 2 weeks later, on June 24. We add 39 weeks and we get a dpa on March 24.
This method is however very indicative because not all women have a 28-day cycle, the ovulation period occurs very rarely at 14 days and, moreover, the spermatozoon can remain in the uterus for several days before. to meet the ovum, as well as implantation (when the embryo produced by fertilization attaches to the wall of the uterus) take more than 24 hours. The true onset of pregnancy can therefore take place days before or after this arbitrary landmark in the cycle.
The weeks of amenorrhea (SA)
Ovulation being too different from one woman to another, doctors and midwives favor another way of calculating the term of a pregnancy, taking as the start the first day of the last period. 41 weeks are added to this date, which is two more weeks than the previous method (the estimated pre-ovulatory period). It is therefore during the week of amenorrhea "AS" that the development of the fetus will be documented during examinations.
Cranio-caudal length (CRL)
Finally, during the first trimester ultrasound, between the 9th and 12th week, the gynecologist will be able to measure the cranio-caudal length, that is to say the length from the head to the buttocks of the fetus, and the diameter of his head. This new data makes it possible to date the onset of pregnancy to within 5 days.
40 or 41 weeks of amenorrhea?
The length of pregnancy is such a bone of contention within the obstetrical medical profession that the baseline may differ from country to country. In France, for example, it is estimated at 41 SA. In Canada, the United States or the United Kingdom, on the other hand, it is only 40 weeks. This variation around the term obviously does not imply a risk for the health of the baby or that of the mother, but can at most upset certain medical and administrative procedures (appointment at the maternity ward, start of your leave, etc. .) if you move from one area to another while you are pregnant.
Up to 5 weeks of term variability
Still referring today, a large-scale study conducted in 2013 by Dr Anne-Marie Jukic, researcher perinatal epidemiologist at the National Institute of Environmental Health Sciences (NIEHS) in Durham in the United States, had arrived, thanks to a follow-up careful, to determine the exact date of the beginning of the pregnancy of 125 women. The results, published in the scientific journal Human Reproduction, revealed that the average time between ovulation and the birth of the baby was 268 days (38 weeks and 2 days) but that it could vary by 37 days (or 5 weeks) from one woman to another.
The notion of term is therefore more a reference than a reality. If a due date is given, it rarely turns out to be conclusive. Labor can begin before or after, and ultimately, on-time delivery only affects about 4% of women.
Weeks, months, quarters
Pregnancy is therefore counted in several units. The months are often the simplest and the most meaningful for those around them, but it is far too vague to represent the true development of the fetus, which should be counted in days as its development is rapid. The weeks are also grouped into 3 quarters thus divided:
- 1st trimester: start of pregnancy (fertilization) at 14 weeks
- 2nd quarter: from 15 SA to 28 SA
- 3rd trimester: from the 29th week to childbirth.
An ultrasound will be performed every quarter. The first, called dating because it allows to better know the date of the beginning of the pregnancy, should be done during the 3rd month. The second, the morphological ultrasound, takes place in the 5th month (between the 19th and the 24th week) and it is this which normally allows the sex of the baby to be known. The third must take place between 28 and 34 weeks of pregnancy (8 months).
The preterm birth
We are going to talk about a premature delivery when it occurs between the 25th week and the 37th week of amenorrhea. Despite everything near term (between 33 weeks and 37 weeks), the baby generally remains without great risk to the health of the baby, who will be monitored and placed in an incubator in the maternity ward. Before that, there are two degrees of prematurity: great and very great. The first designates births between the 28th and 32nd week and involves special care for the baby who will be transferred to the neonatal resuscitation unit of a type 3 maternity unit. This is also where babies will be taken care of. very premature babies, born before 28 weeks (6 months of pregnancy), whose extremely fragile health requires constant monitoring.
Exceeding the term
Pregnancy that is several days longer than expected is not uncommon and is usually safe. Induction is not necessary since in the majority of cases labor begins naturally within days of dpa. If the delivery has still not taken place after the 41st week of amenorrhea, then we will talk about overdraft and the pregnancy will be monitored.
Risks may appear for the baby, such as the aging of the placenta (placental senescence) which can deprive him of the necessary amount of oxygen and nutrients, or the lack of amniotic fluid. An ultrasound can be done every 2 or 3 days to check for abnormalities, as well as an amnioscopy (checking the color of the amniotic fluid).
The induction of childbirth
Overcoming pregnancy, even without complications, becomes worrying after a certain stage. If labor has still not started at 42 weeks, doctors will induce labor with an intravenous infusion of oxytocin, sometimes combined with the application of a gel containing prostaglandins when the cervix is too closed. Both substances are of course safe for the baby or the mother. When the expansion is optimal, the water bag is pierced to activate contractions and labor.
The induction may not be enough to induce the birth, in which case it is done by cesarean section.
How to prepare for childbirth?
You will understand, the term and expected date of delivery only offer an estimate of the length of pregnancy. It is your body and your child that will really determine it. So do not necessarily wait for these dates to be attentive to the warning signs of his birth.
If the baby does not decide to be too early, the expectant mother is normally on maternity leave and probably very tired from the hormones. This is one of the reasons why it is advisable to prepare your maternity suitcase well in advance, but also to prevent it from ending up hastily and incomplete.
The best-known symptoms are not necessarily those which presage the arrival of the child. Contractions are certainly a very important clue, but while they are not accompanied by dilation of the cervix, they do not signal that labor has started. Some can be very painful, regular, and last 2 to 3 hours before coming to a complete stop. We then speak of false labor contractions. If in doubt, however, it is preferable to consult or go to the maternity ward. Likewise, the loss of the mucous plug, which protects the bag from water does not mean that childbirth is imminent. Some mothers lose it days before, or even during labor. This can also be the case for the pocket of waters, although this is rare.
The loss of water, she announces that baby will arrive soon. More importantly, it means that he is no longer protected against infections. It may rupture completely and release all of the amniotic fluid, or it may just crack and only leak a discharge. In both cases, it should not be long before you go to the maternity ward. You can wait for the first contractions to appear but certainly no longer! This phase is called pre-labor. Then comes labor with a very strong intensification of the contractions. Its duration will depend from woman to woman but also whether it is a first child or not, as the following ones are often faster. Usually, it takes an average of 8 hours between the start of contractions and childbirth.
Monitor her pregnancy
Being pregnant is the start of a great adventure that requires a little planning, however. Calculations of early pregnancy and dpa will notably result from several important medical appointments to check that everything is going as well as possible and that the fetus is developing normally.
Even if your doctor is responsible for ensuring follow-up, it is convenient and recommended from the start to keep a pregnancy diary or a personalized calendar that will allow you to note all the key dates, whether they are ultrasounds, from the start of the maternity ward or the major stages of your child's development. Viewing the entire course of her pregnancy is often a good way for parents to calmly anticipate the birth of the baby.
Knowing the term of pregnancy and the expected date of delivery is also essential to determine the start of maternity leave.
And why not through an online tool or an application?
Appointment with the gynecologist, meeting with the midwife, preparatory courses for childbirth, the start of maternity leave … Do all these dates make you dizzy in advance and you fear forgetting them? Do not panic !
It is to accompany you throughout this wonderful experience of motherhood that aufeminin has created pregnancy monitoring, week by week. Future parents will be able to find precious advice on the evolution of their baby but also on things to watch for in the mother, foods to avoid or favor and the steps to take to be on time for medical examinations and administrative requirements.
Many applications have also emerged to make the lives of pregnant women easier, from the start of their pregnancy and throughout its duration, or even after the birth of the baby in order to follow its first months of life.
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