When a couple finds out that they are expecting a baby, the first thing they do is do the math to calculate the probable date of delivery and know what will be the day when the offspring will arrive in the world. Some argue that it makes more sense to talk about probable weeks of delivery, given that fewer than five percent of babies are born on the probable date of delivery (PPD) .
How is the expected due date calculated?
The average duration of pregnancy is 280 days or 40 weeks from the beginning of the last menstrual period (LMP) and 266 days from the date of conception, although the pregnancy is considered to have come to term after week 37 (259 days). If the woman reaches week 40 and has not yet gone into labor, it could wait until week 42 to induce it, thus giving more time for labor to start naturally.
To estimate your expected due date (FPP) you can do a simple calculation, a formula known as Naegele’s Rule. It consists of subtracting three months and adding seven days to the first day of your last menstruation (LUM). The result is your due date.
For example, if your last period was on January 3, you have to subtract three months, and add seven days: the probable due date is October 10. (Below we leave you a table to calculate it more easily).
But this rule is based on regular 28-day cycles, in which fertilization has occurred in the middle of the cycle, that is, two weeks after the date of the last rule, something that does not always occur. In the case of irregular periods or when fertilization takes place before or after day 14 of the cycle, the date may vary .
Probable (or unlikely) due date
A large study conducted in Australia in 2013 with data from more than 18,000 spontaneously laboring pregnant women found that only 5 percent of births occurred on the expected date of delivery , regardless of prenatal check-ups.
Additionally, they were able to verify that approximately 66 percent of the births occurred within seven days of the expected due date.
For its part, according to data from the Perinatal Institute, a UK non-profit organization, the percentage is even lower: only four percent of babies are born on their expected due date.
The figure is slightly higher (4.4 percent) when preterm births and pregnancies with complications are not included. Of the rest, more than 90 percent are born in the range of two weeks before or after the expected date.
According to a study conducted in Sweden in 2013, most new mothers give birth between three and five days after their due date.
What if I have irregular cycles?
In the case of irregular cycles, the calculation is more complicated, since it is not possible to estimate the ovulation date with the same precision as if the woman had regular cycles.
For those cases, the American College of Obstetricians and Gynecologists says that fetal measurements taken by first-trimester ultrasound are the most accurate way to estimate delivery date.
Factors influencing the duration of pregnancy
A full-term pregnancy is one that occurs between weeks 37 and 42 of gestation, a wide margin beyond the exact date that is stipulated as the probable date of delivery (PPD). There are many factors that can influence whether the baby arrives earlier or later.
For example, a study of more than 40,000 women in London published in 2016 found that if a woman’s first baby arrived before or after her due date, her second baby tended to do the same, but not for as many days.
It also influences the genetic inheritance, diseases and lifestyle of the mother or complications in pregnancy such as diabetes or high blood pressure, factors related to a greater probability of giving birth before the expected date.
The important thing is not the exact date
Bottom line : don’t take your due date at face value. While parents may find it helpful to know the exact date their baby will be born, it is often impatient and anxious to see that the date is approaching and there are no signs of delivery.
Therefore, it is important that you know that it is an estimated date of when your child will arrive , and the main objective of this date is to carry out all the prenatal controls that correspond to each stage of development.
In Babies and more | Scheduled delivery? Why it should take place beyond 39 weeks, Due Date Calendar (FPP)
