Why pregnancy lasts 9 months

If your pregnancy lasts more than 42 weeks, it is called post-term past due. This happens in a small number of pregnancies. While there are some risks in a post-term pregnancy, most post-term babies are born healthy. Your health care provider can do special tests to check on the health of your baby. Keeping a close eye on the baby's health will help increase the chance of good outcomes.

Many women who go past 40 weeks are not really post-term. Their due date was just not calculated correctly. After all, a due date is not exact, but an estimate. Your due date is estimated based on the first day of your last period, the size of your uterus womb early in your pregnancy, and with an ultrasound early in pregnancy.

When a pregnancy truly is post-term and goes past 42 weeks, no one knows for sure what causes it to happen. The placenta is the link between you and your baby.

As you pass your due date, the placenta may not work as well as before. This could lessen the amount of oxygen and nutrients that the baby gets from you. As a result, the baby:. If you reach 41 weeks 1 week overdue , your provider will do tests to check on the baby. These tests include a non-stress test and biophysical profile ultrasound. When you reach between 41 and 42 weeks, the health risks to you and your baby become even greater.

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Your Guide to the Second Trimester of Pregnancy. Your Guide to the Third Trimester of Pregnancy. How to Calculate Your Due Date. View Sources. March of Dimes, What is Full Term? Week by Week. Pregnancy Groups. First Trimester. Jump to Your Week of Pregnancy. Pregnancy Week. 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.

Some clues to the length of gestation include:. The general procedure for a pregnancy ultrasound includes:. A baby born prior to week 37 is considered premature. 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:. Around five out of every 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:. 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.