How many weeks does pregnancy last?

How many weeks does pregnancy last?

Sam Baby Health Baby Mother 217

Normally, pregnancy lasts 9 months. But some women give birth earlier, some later. In the article, we will consider the norms for the duration of pregnancy in women, the causes of premature and late birth and what affects their timing.

Norms of the duration of pregnancy

If the expectant mother knows the date of the last menstruation, she even before registering with the antenatal clinic calculates when her baby is approximately born. But often the calculations of the woman and the gynecologist do not coincide. Why is that?

The fact is that there are 2 terms:

  1. Obstetric. Gynecologists focus only on him. The duration of pregnancy is calculated by the last menstrual period before conception. And it is he who is taken into account during pregnancy, ultrasound, analysis, and measurements of the parameters of the child himself. As a rule, women remember when they had their periods, therefore this calculation is more accurate;
  2. Embryonic. This period lags behind obstetrics by 2 weeks. The fact is that when calculating it, the date of the last menstruation is not taken into account. The countdown begins from conception.

On average, the duration of pregnancy for the embryonic period is 38 weeks, and for the obstetric period – 40 weeks. Childbirth can start 2 weeks earlier or later, that is, at 38 – 42 weeks. This is considered the limit of the norm.

What determines the duration of pregnancy

There are a number of factors that affect the length of gestation.

The first factor is the woman’s health. Women with a healthy reproductive system and the body as a whole, who have not had abortions, miscarriages and other pathologies of pregnancy before, have every chance of giving birth to a full-term baby. If a pregnant woman has chronic diseases or she fell ill while in a position (for example, an infection), this may affect the duration of the pregnancy.

The second factor is age. Young girls often give birth to children earlier, and mothers between the ages of 30 and 35 are more likely to postpone pregnancy.

The third factor is the number of births in the past. Women who have already had childbirth give birth earlier than those who enter the delivery room for the first time.

The fourth factor is the course of pregnancy. This includes any deviations from the norm: presentation and placental abruption, early maturation of the cervix, preeclampsia and other conditions of the expectant mother that require early delivery.

The fifth factor is socio-psychological. Pregnant women who are nervous, lead an unhealthy lifestyle, work in hazardous industries, live in constant stress or an unfavorable environment, eat poorly, risk giving birth to their baby at the wrong time.

The sixth factor is the condition of the fetus. Body weight, hormonal status, bone density – all this affects the duration of pregnancy and the readiness of the baby to be born.

The influence of the placenta on the duration of pregnancy

The placenta plays a huge role in the course and duration of pregnancy. Through it, oxygen and nutrients are supplied to the child, it acts as the baby’s excretory system.

Scientists from the University of Durham conducted a study that compared the placenta of mammals of different species. They came to the conclusion: the placenta, connecting the mother and the fetus, affects the duration of pregnancy. And it depends on the structure of the placenta itself: the more complex it is, the faster the gestation period ends. In women, it has a simple structure, less nutrients for the fetus pass through it – which is why the intrauterine development of human children takes as long as 9 months. If the condition of the placenta is not normal, then the duration of pregnancy can be sharply reduced or, conversely, increased.

What is premature birth

In 5 – 12% of cases, babies are born prematurely – at 22 – 37 weeks and weigh 1 – 2.5 kg. Previously, childbirth was considered premature from the 28th week, and everything that happened before it was considered a miscarriage. It was impossible to go out and save such crumbs.

But medicine does not stand still, new methods of nursing premature babies are being introduced in obstetrics. Therefore, the World Health Organization has expanded the framework: now babies born from the 22nd week have a chance at life. In modern perinatal centers, babies are nursed in extremely low body weight – only 0.5 kg.

Types of early birth

Distinguish between threatening and incipient labor.

Threatening labor can be brought under control and prevent true labor. With the right therapy, a woman can deliver and give birth on time. They can be suspected with such symptoms: pulling pain in the lower back and lower abdomen, traces of blood on the pad, the fetus may be more active than usual. In such a situation, you need to urgently call an ambulance.

The onset of labor cannot be controlled – in this case, there is no turning back. The cervix opens 4 cm or more, regular contractions appear – starting with a frequency of 10 minutes, which contracts, the fetus moves along the birth canal. In this case, the task of the obstetrician is to correctly carry out childbirth and take the baby.

Causes of early birth

The factors that affect the duration of pregnancy and the premature birth of a baby can be divided into 2 groups.

The first is socio-biological factors. These include:

  • bad habits during gestation – alcohol, nicotine, drugs, as well as taking drugs that harm the fetus;
  • unhealthy lifestyle – poor or unhealthy diet, passive lifestyle, weight problems (excess or deficiency);
  • difficult working conditions – for example, night shifts, physical labor, harmful working conditions (vibration, noise, toxic substances);
  • emotional state – stress, anxiety, excitability or depression, unfavorable social environment or family atmosphere affect the duration of pregnancy.

Women who lead an unhealthy lifestyle or do not take care of themselves during pregnancy often have premature babies.

The second group is medical factors. These include chronic diseases, previous abortions and miscarriages.

Another reason is pregnancy complications. For example, gestosis in the third trimester, Rh-conflict between mother and fetus, or failures in a woman’s immune system, when her body perceives the fetus as foreign and tries to expel it.

Other medical factors also affect the duration of pregnancy. Let’s talk about them in more detail below.

Infectious diseases in a woman

Some infections can cross the placental barrier and affect the fetus. Infection of the fetus leads to developmental disabilities, postnatal health problems and premature birth.

Such ailments include transmitted infections, as well as inflammatory processes in the genitourinary system, kidneys or lungs. Women diagnosed with chlamydia, herpes, gonorrhea, and trichomoniasis is at risk.

Isthmico-cervical insufficiency

If the cervix ripens faster, it opens earlier, so it cannot hold the fetus. This shortens the duration of the pregnancy.

Premature outpouring of water

When the water leaves, the release of prostaglandins occurs. These hormones trigger the birth mechanism.

Anatomical features of a pregnant woman

In some women, the structure of the uterus is different from most. In such cases, the duration of pregnancy may be less than normal.

Pregnancy pathologies

These include previa or placental abruption, for example. In the first case, a woman is usually placed in a maternity hospital for storage, since she may have massive bleeding at any time. With placental abruption, the same thing happens, so the woman needs emergency medical attention.

By itself, placental abruption is not a sign of labor. It’s just that if it happens at a later date, then doctors save not only the life of the woman in labor, but also the child.

Forecasts for children

If the baby was born between the 22nd and 28th weeks, he has a chance to survive, but the prognosis is not the most favorable: health complications cannot be avoided. For babies born from 28 to 33 weeks, the prognosis is slightly more positive: thanks to drug therapy, their lungs mature faster and better. Well, babies who gave birth from 34 to 37 weeks have the most chances.

What is delayed labor

If a woman has not given birth before 42 weeks, then such a pregnancy is assessed as post-term, and the baby is assessed as “overripe.” These babies are usually longer, but they have less subcutaneous tissue. This is a sign of postmaturity. If the baby does not have these signs, then the pregnancy is assessed as prolonged. This situation occurs in 10% of women in labor.

Signs of post-term pregnancy

She is diagnosed based on an assessment of the condition of the mother and the fetus.

From the mother’s side. The woman’s body is not ready for labor, the abdominal circumference has become smaller, the height of the uterus has increased, aging of the placenta and fetoplacental insufficiency are noted, the amniotic fluid becomes cloudy, with an admixture of meconium.

From the side of the fetus. The bones of the skull have become denser, fontanelles, sutures and subcutaneous fat layer have decreased, vellus hair and cheese-like lubricant are not present. The weight of the fetus exceeds 4 kg, it grows by 2 – 3 cm. Such crumbs may have heart rhythm disturbances: arrhythmia, extrasystole.

Another criterion is labor. It can start, continue for a day, and then stop and not resume within a week.

If the duration of the pregnancy exceeds 42 weeks, the woman is examined at the maternity hospital. If, when assessing the condition of the fetus, it is revealed that it is suffering in utero, then labor is caused or a cesarean section is performed.

Why is the baby born later?

Doctors name several reasons why waiting for a baby can be delayed.

First, the age of the woman in labor. Mothers over 30 tend to postpone pregnancy.

Secondly, menstrual irregularities. For example, if a woman incorrectly named the date of the last menstrual period or does not remember it at all, then an error in calculating the DA is quite possible.

Thirdly, diseases. Inflammatory processes in the genitourinary system can both cause premature birth and delay the birth of a baby. Therefore, pregnant women with chronic ailments need to be doubly careful to avoid exacerbation.

Fourth, the characteristics of the mother’s body. Infantilism of the genitals, lack of generic dominant, endocrine system disorders, hormonal insufficiency of the placenta. Another reason is the peculiarities of the central nervous system. Often the same mothers postpone pregnancy.

Fifth, the condition of the fetus. Babies with disorders of the pituitary-adrenal system or defects are born later.

Baby predictions

Delivery of post-term babies is fraught with injuries, since their skull bones are denser and less compressed during the passage of the birth canal. Therefore, such newborns are at risk for traumatic brain injury.

Another complication is hypoxia. During the birth process, babies experience oxygen starvation. But those born at 40 weeks of age tolerate it more easily than those born at 42 and later. The latter have a more complex nervous system, so it is more difficult for them to adapt to oxygen deficiency.

Post-term infants are at risk for perinatal diseases and mortality.


Both miscarriage and prolongation are dangerous for the fetus and the expectant mother. In each case, a detailed analysis of the situation and a balanced decision on the tactics of managing a pregnant woman are required. Therefore, contact your obstetrician-gynecologist in time if something bothers you. With timely medical care, the prognosis is favorable, and the likelihood of having a healthy baby is maximum.

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