Average Pregnancy Length For First-Time Mothers

What about the risk of stillbirth?

This section will discuss how the risk of stillbirth rises as pregnancy progresses.

When learning about stillbirth rates, there are two things you must comprehend.

First, absolute risk and relative risk are distinct from one another.

For instance, if there was a 1 percent absolute risk of stillbirth at 41 weeks, 7 out of 1,000, then that means that 1. Seven mothers out of every 1,000, or 17 out of 10,000, will give birth still.

If someone said that the risk of having a stillbirth at 42 weeks compared to 41 weeks is 94% higher, then that sounds like a lot However, some individuals might believe that the risk is still low in absolute terms—1 7 per 1,000 versus 3. 2 per 1,000.

Yes—3. 2 is about 94% higher than 1. 7, if you do the math! So, while it is a true statement to say %E2%80%9Cthe risk of stillbirth increases by 94%,%E2%80%9D it can be a little misleading if you are not looking at the actual numbers behind it

For advice on how healthcare professionals can bring up the possibility of stillbirth, please see our handout on Talking about Due Dates for Providers.

The second crucial concept you must comprehend is that there are various methods for calculating stillbirth rates. You may obtain different rates depending on the method used to calculate the rate.

How long is a normal pregnancy? Is it really 40 weeks?

In the U. S. It is impossible to know exactly what percentage of people today would naturally go into labor and give birth before, on, or after their estimated due date because induction is common in the United States and other Western countries at or even before 40 weeks.

In the past, researchers studied a large group of pregnant women, measuring the time from ovulation (or the last menstrual period, or an ultrasound) until the date the person gave birth, and calculating the average length of a normal pregnancy. However, this approach is flawed and does not produce reliable results.

So how can we deal with this problem?

Today’s researchers employ a technique known as “survival analysis” or “time to event analysis.” This unique approach enables you to include all of these individuals in your research while still obtaining a reliable estimate of how long it typically takes for a person to enter spontaneous labor. Two studies have used survival analysis to gauge the typical duration of pregnancy:

Smith examined the duration of pregnancy in 1,514 healthy women whose estimated due dates, determined by the first day of the last menstrual period, were exact matches with the estimated due dates from their first trimester ultrasound in a very significant study published in 2001 (Smith, 2001a).

The researchers found that 50% of all women giving birth for the first time gave birth by 40 weeks and 5 days, while 75% gave birth by 41 weeks and 2 days

Meanwhile, 50% of all women who had given birth at least once before gave birth by 40 weeks and 3 days, while 75% gave birth by 41 weeks

This means that the conventional “estimated due date” of 40 weeks was incorrect for both first-time and seasoned mothers in Smith’s study.

Using Naegele’s rule, the actual pregnancy was about 5 days later than the expected due date in a first-time mother and 3 days later in a mother who had previously given birth.

In 2013, Jukic et al. analyzed survival data to determine the average duration of pregnancy. Only 125 healthy women participated in this smaller study, which was conducted between the years 1982 and 1985. However, this study was also significant because it tracked the participants’ hormone levels daily for six months before conception (Jukic et al. , 2013).

This indicates that the researchers were aware of the precise dates on which the participants ovulated, gave birth, and even had their babies implant!

So how long did pregnancies last on average in this study?

The final sample of 113 women had a median time from ovulation to birth of 268 days (38 weeks, 2 days after ovulation) after excluding women who had preterm births or conditions related to pregnancy.

The median amount of time between the first day of the last period and birth was 285 days (or 40 weeks and 5 days).

Pregnancy durations ranged from 36 weeks and 6 days to 45 weeks and 6 days after the last period for one woman. Although it may seem like a long time—45 weeks and 6 days—this particular woman gave birth 40 weeks and 4 days after ovulation. Her ovulation did not follow the expected pattern, so her LMP due date was unreliable.

The researchers also found that:

  • 10% gave birth by 38 weeks and 5 days after the LMP
  • 25% gave birth by 39 weeks and 5 days after the LMP
  • 50% gave birth by 40 weeks and 5 days after the LMP
  • 75% gave birth by 41 weeks and 2 days after the LMP
  • 90% gave birth by 44 weeks and zero days after the LMP
  • Remember though, some of the participants did not ovulate on the 14th day of their period (that%E2%80%99s why you saw the statistic that 10% still haven%E2%80%99t given birth by 44 weeks after the LMP!) So if we look at when people give birth after ovulation, you%E2%80%99ll see this pattern:

  • 10% gave birth by 36 weeks and 4 days after ovulation
  • 25% gave birth by 37 weeks and 3 days after ovulation
  • 50% gave birth by 38 weeks and 2 days after ovulation
  • 75% gave birth by 39 weeks and 2 days after ovulation
  • 90% gave birth by 40 weeks and zero days after ovulation
  • Longer pregnancies were more likely for women whose embryos took longer to implant. Additionally, on average, the gestation period was 12 days shorter in women who experienced a particular hormonal reaction soon after conception (a late rise in progesterone).

    5 FIRST TIME MOM MISTAKES TO AVOID During Pregnancy + Labor

    Leave a Comment