Whenever you think about the typical length of pregnancy, nine months instantly comes to mind.
It’s what we’re all told, time and time again, about how long you can expect to – ahem, expand – before your tiny (or not-so-tiny) baby wants to evacuate your body.
Well, it turns out that most pregnancies are not really nine months. In fact, there’s a lot of variation going on – so while some could last nine months, others could be hitting the 10-month mark. And for most, it might actually be more like... eight.
Pregnancy is typically counted from the first day of your last period, rather than the date when the baby is actually conceived (which is usually about two weeks later).
In the UK, you’ll typically have an ultrasound scan at 12 weeks which might alter your estimated due date by a few days depending on how developed your baby is.
When you’re pregnant, your due date is typically calculated in the 40th week of pregnancy, which you might consider to be nearer 10 months than nine.
But this isn’t really the case either because of the variation in month length.
As What To Expect explains: “Four weeks is 28 days, but months (with the exception of February, of course) have 30 or 31 days, making each month about 4.3 weeks long.”
How long is the typical pregnancy then?
Studies have found the average time a baby spends in the womb – from ovulation to birth – is 268 days. That’s 38 weeks and two days.
Or, as Business Insider calculates: 8 months, 24 days and 16 hours. Yup, so not nine months, or 10, but rather... eight?!
But this can vary dramatically from person to person. In fact, one study determined the variation here was 37 days. So if you and another person were given the same due date, you could give birth on one day, and they could give birth 37 days later.
Some factors that were found to lengthen a person’s pregnancy, included:
- Conceptions that took longer to implant
- Pregnancies with a rapid progesterone rise
- Older mothers
- Mothers who had longer pregnancies previously
- Mothers who were heavier at birth
According to InformedHealth.org, around 60 in 100 women give birth on or before their due date.
In 35 out of 100 women, contractions start on their own within two weeks of the due date. And for five in 100 women, the pregnancy can last even longer.
“Almost all babies are born within three or four weeks of the due date,” according to InformedHealth.org.
“If a baby hasn’t been born by then, the risk of being stillborn increases. Babies are very rarely born that late, though, because labour is usually induced two weeks after the due date at the latest.”
Well, now you know.