Does Giving Birth “Reset” a Woman’s Fertility?

Does giving birth “reset” a woman’s biological clock? Perhaps. Women who have given birth before do have a better chance of getting pregnant in their mid to late 30s.

Do couples have an easier time getting pregnant after they have already had a child?

I’ll confess, my interest in this topic is personal. We were one of these couples. We took over a year to conceive my son, but our second was a surprise.

Back when my first was born, as we were getting ready to head home after three long days in the hospital, with round-the-clock wake ups, I made the mistake of telling our delivery nurse that we were not planning to use birth control.

She immediately launched into a lecture that we needed birth control. “Giving birth can reset your fertility,”  she stated matter-of-factly. And then added sternly that we needed to start using birth control as soon as we resumed having sex.

Although she briefly made me feel like an errant teenager, I did not take her advice very seriously.

Various reputable sources of medical information, such as WebMd, state that the prior births do not “reset” a woman’s fertility,asserting that the notion is a myth.

Two recent studies, however, suggest there might be something to this idea after all.

Kenneth Rothman of Boston University, led a prospective study, which followed 2820 Danish couples who were trying to conceive for up to 12 cycles.

Rothman then calculated how the woman’s age affected a couple’s fecundability ratio–a statistical estimate of a couple’s ability to conceive each menstrual cycle.

Couples in which the woman had given birth before–about half of the couples in their early 30s and two-thirds of those in their mid to late 30s–had much higher fecundability throughout their 30s:

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Continue reading “Does Giving Birth “Reset” a Woman’s Fertility?”

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Giving Birth Takes Twice As Long It As It Did 50 Years Ago

Giving birth today takes twice as long as it did 50 years ago, and this can affect your chances of a c-section.

My first labor was long. Really long. It lasted from Friday night to Sunday evening. Pain I had anticipated, prepared for, given myself multiple pep talks for, but the duration… It undid me.

As I recently watched a good friend go through a similar labor, some old nagging questions resurfaced: How uncommon is it for women to labor for days? What is a “normal” length of labor, if such a thing exists?

Oddly enough, the medical answers to these questions have just changed dramatically. This is because of a recently completed landmark study of nearly 100,000 labors. The study, which used medical record data collected between 2002 and 2008 from hospitalsm across the U.S., showed unequivocally that we labor much more slowly than we used to. Much, much more slowly.

In fact, our labors have slowed down so much that in 2014 the American College of Obstetricians and Gynecologists (ACOG) revised its definitions of normal and overly slow laborUntil then, the definitions were based on data from the 1950s and 1960s. These data were used to define a “normal” labor duration, how long it takes most women in active labor to reach a full 10 cm of dilation and then to push the baby out. By the same token, these data were used to defined abnormal labor: labors that lasted longer than 19 out of 20 of these labors (the 95th percentile for duration) were considered overly slow or stalled.

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Inducing Labor Past 39 Weeks Does Not Increase Your Chances of Having a C-Section

Pregnant women often fear that having their labor induced will lead to a c-section. In her bestselling book, Expecting Better, Emily Oster cites fear of a c-section as the primary reason she opted not to have her labor induced. Other reputable sources like the Mayo Clinic Online and March of Dimes claim that inductions increase the odds of a c-section.

But, according to the latest scientific research, these fears are unfounded. Past 39 weeks, labor inductions do not appear to raise the risk of having a c-section. Instead, being induced lowers your chances of a c-section by about 20%.

How did we get this so wrong? Until about 5 years ago, almost all the evidence on inductions and c-sections came from observational studies, which were all subtly biased, because they compared women who went into labor on their own with women who were induced.

What was wrong with this comparison?

Observational studies typically control for gestational age. This means that, in effect, they match women by the week they delivered, because the risks associated with giving birth climb as pregnancies continue past 39 weeks. Women who went into labor spontaneously at 39 weeks were compared to women who were induced at 39 weeks, and so on.

And, when matched by delivery week, women who go into labor spontaneously are less likely to have c-sections.

So what’s the problem? Pregnancies that go into labor spontaneously by a certain week are different from those that don’t.

Think about it this way: What is choice women actually face past 39 weeks? Women cannot will themselves into labor, or there would be a lot fewer pregnancies going past 40 weeks. Instead, pregnant women can only choose either to be induced or to wait it out.

So the proper study design compares these two options: being induced versus waiting it out. This is the approach taken by recent randomized controlled trials on inductions.

In these trials, pregnant women are randomly assigned to be induced past a certain point in pregnancy, for example, at 41 weeks, or to wait it out. Women assigned to wait may go into labor on their own or be induced at a later date. Using this approach, studies find, almost without exception, that relative to waiting and delivering at a later point in pregnancy, inducing labor leads to a lower chance of a c-section.

A 2009 meta-analysis (combined analysis of multiple studies) was the first to convincingly reveal the problem.

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The analysis compared the results of observational studies and randomized controlled trials (RCTs). The observational studies found a roughly 20% increase in the risk of c-section following inductions; the better-designed RCTs found a roughly 20% reduction in the risk.

Continue reading “Inducing Labor Past 39 Weeks Does Not Increase Your Chances of Having a C-Section”