How Many Weeks Is A Human Pregnancy

What is the average pregnancy length for first-time parents?

While your due date may give you a better idea of how far along you are in your pregnancy, it is impossible to know with certainty when your baby will be born unless you are having a planned C-section.

“Most people deliver between 39 and 41 weeks,” says Dr. Celestine. “But statistically, first pregnancies are likely to be a little longer.” Research into how long pregnancy is has varied. One analysis highlighted that 15% of first babies are likely to arrive after 40 weeks, compared to 10% of subsequent babies. However, the same study noted that 12% of first babies were likely to be born before 37 weeks compared to 10% of other babies.

Therefore, it’s important to keep in mind that while your due date may give you a general idea of when your baby will be born, there’s no way to be certain until the big day actually arrives.

Does an irregular cycle affect your due date?

If you have an irregular cycle, tracking your period may be a little more challenging. However, if this is something you experience, don’t worry. An irregular cycle won’t affect the length of your pregnancy. Because many people have irregular cycles, we occasionally can’t use your period as a predictor. Instead, we must use an ultrasound to measure the fetus, says Dr. Celestine.

During your first trimester (the first 14 weeks of pregnancy), how far along you are (gestational age of pregnancy) is determined by your baby’s crown-rump length. “This is literally the length of the fetus as seen on the ultrasound,” explains Dr. Celestine. Your health care provider will note how long your baby is in centimeters from the top of their head (crown) to the bottom of their buttocks (rump).

“This gives us the estimated gestational age,” adds Dr. Celestine. Your health care provider can take these measurements between weeks six and seven of pregnancy up until week 14. After week 14, your gestational age is determined by other methods (including measuring your baby’s head circumference, abdomen, and thigh bone). This is called biometry.

Your doctor may compare the information from your first ultrasound with the anticipated due date based on your most recent period. Your healthcare provider may give you a few estimated due dates in the initial weeks after learning you’re expecting, as they work to determine the most precise estimate. To keep track of your pregnancy, confirm that you and your doctor are using the same due date.

It’s important to remember that whether you’re working from the first day of your last period or the crown-rump length on an ultrasound, a due date is just a rough estimate of when the baby will come. “It can be off by a few days, either way,” says Dr. Celestine. Most babies are born between 38 and 41 weeks of pregnancy. In one study of nearly 19,000 women in Australia, just 5% of births actually happened on their due dates. The due date is more of a guide to track how far along you are in your pregnancy than a set-in-stone deadline of when your baby will arrive.

Why is pregnancy calculated from your last period?

Using your last period is just a more accurate benchmark to date a pregnancy from, so why start the clock on pregnancy before sperm even meets egg (and, actually, before your ovary even dropped the fated egg that made your baby)? You probably won’t be able to pinpoint the precise moment of conception, even if you are an expert on cervical mucus, are certain of the day you ovulated, and know the day or days that you had sex.

This is due to the fact that there is a larger window than you may realize: sperm can wait for three to five days after they arrive for an egg to fertilize, and an egg can be fertilized for up to 24 hours after it has been released. That’s also good news because it means that by the time you miss your period, you will already be four weeks pregnant.

How long does a pregnancy last? – Dr. Madhushree Vijayakumar

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