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:

Screen Shot 2015-02-03 at 12.27.21 PM

Until about age 30, women who had never given birth have roughly the same fecundability as a 20-year-old. Starting sometime in their early 30s, though, their fecundability begins to decline. By 35, the fecundability of women who have never given birth is significantly lower than the average 20-year-old’s.

The picture is more encouraging for women who had one or more births under their belts. Their fecundability remained higher than a 20-year-old’s through their mid-30s.

(Note that the curves above are based on estimated fecundability at three ages–25, 30, and 35–and therefore are not informative about what happens after 35.)

second study, led by Geoffrey Howe of Oxford University, paints a very similar picture. Instead of fecundability ratios, Howe used a different–and arguably superior–measure of fertility: how long it took women to give birth.

Howe tracked 17,032 women in their 20s and 30s who attended family planning clinics in Scotland and Great Britain. From 1968 to 1983, 4,108 of these women stopped using birth control in order to have a baby. 

Here’s how long it took women who had never given birth before to have a baby:

Screen Shot 2015-02-03 at 11.46.49 AM

As you can see, starting around age 34, women who have not given birth before took longer to become pregnant.

In contrast, women who had given birth before conceived quickly until around 38. Even at 38 or 39, they still had better chances than the 34-to-35-year-olds who had not given birth before.

Screen Shot 2015-02-03 at 11.46.24 AM

Just like in Rothman’s study, the fertility of women who had never given birth declined earlier, in their early 30s, and dropped off more steeply than the fertility of women who had given birth before, which did not show much of a decline until they were 38.

The difference between these groups of women is striking. By the test of fertility that arguably matters the most–ultimately ending up with a baby–women who had given birth before and started trying for another at 40 were better off than were women who had never given birth before but started trying at 36 or 37 (18% did not have a baby after 60 months versus 25% did not have a baby after 60 months).

(These percentages sound scary. But these numbers probably overstate a woman’s current chances of remaining childless, as infertility treatments have advanced considerably since the 1970s and 1980s.)

The Bottom Line

Do these two studies prove that giving birth “resets” a woman’s fertility? Can giving birth turn your biological clock back several years?

Not exactly. These studies demonstrate a link between having given birth before and being able to conceive later in life; they do not establish causation.

What else might be going on? Well, selection bias, for one.

Couples who have had a child in the past tend, as a group, to be more fertile than couples without children. This is because of sorting that occurs during the early reproductive years. During this time, the less fertile will tend to remain childless, while couples of high fertility will be more likely to conceive quickly or by accident. So, by the time the group without children reaches their mid-30s, they disproportionately include the less fertile.

But regardless of the underlying reason, the upshot is the same: if you have already had a baby, your chances of having another one in your mid to late 30s look pretty good.

This post is the first in a series of posts on different aspects of fertility–miscarriage, infertility treatments, and male fertility issues, among others. If you have a story about getting pregnant–or about struggling to get pregnant–I would love to hear from you. You can share your story in the comments or message me privately at @xpectingscience on Twitter.

Did you have an easier time conceiving after giving birth?

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Author: Amy Kiefer

I am a research scientist and mother of three munchkins. I live in the Bay Area and when I am not child wrangling and catching up on lost sleep, I love digging into the research on all things fertility, pregnancy, and breastfeeding related.

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

  1. I love your posts. As you’ve said, it is surprisingly difficult to find high quality information based on science for these topics! I am a 38 year old woman, pregnant with my second child. I would love if you could summarize the research on the risks for babies and moms past age 35. All articles start with the things that can go wrong and give the impression that is the typical experience of a pregnant woman of my age. However that does not match my experience of staying quite healthy. Also, it seems that statistically, most women have healthy babies, but that is not mentioned either. Finally, quality information about prenatal testing, especially non-invasive prenatal testing is difficult to find. I would love to see you tackle these topics. Thank you for providing such a fantastic resource for critically thinking parents!

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  2. What a briliant article, I had my first child at 34 and my son is just coming up to 5, I also had a second child at 37 but sadly she was born prematurely and was too poorly and only lived 7 months. So we are trying again I fell with trying with my son after 8 months and fell after 3 years with Amelia without actively trying. So the reason we also find it hard is my partner had the snip when I meet him but got it reversed for me, so I think the statistics in our case in regards to time it took are pretty good.
    Just wanted to say thank you for this enlightening article as now I am 39 and feel time is of the essence! But anyway seen my Doctor getting lots of support so fingers crossed x

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  3. Well, it took me nearly 2 years and IVF to get pregnant with my first. Then, one period and bam pregnant with my second. So, my experience supports the claim. I am sure it depends on your reason for infertility. Mine was mild endometriosis, which some professionals say (not necessarily the research) can be ‘cured’ by pregnancy (a bit cruel when you can’t get pregnant). In my case, not ovulating for almost 2 years during pregnancy and breastfeeding did probably knock back my endo and ‘reset’ my hormones… Maybe if research drilled that far in depth maybe a pattern would emerge?

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  4. We had our first son with fertility help at age 35 using artificial insemmination. Unfortunately, I was unable to conceive for the second child we wanted so much until seven years later using IVF and many cycles of failure. I have endometriosis as well. In fact our fertility specialist told us we only had a 2-3% chance of success with baby #2. She might as well have said – you are Infertile. So of course, we were ecstatic when I got pregnant and given the difficult journey to have our second child – seven years and lots of tears – I then promptly told the world we had just had our last baby. Many folks have been asking if we wanted more children. Even though we want to do one more, duction was probably the best route.

    So while breast-feeding, I was surprised with my period came. I did some research and discovered that if your infant sleeping through the night and you do not continue to extract what he sleeping, the chance of relation is possible. However since we have had seven years of unprotected sex choose any children and required several rounds of IVF before we had one I wasn’t served when we had unprotected sex. A few weeks later I felt pregnant but that didn’t make sense and it wasn’t possible so I had been told. Still I’m not quite sure what forced me to go get a pregnancy test but I did. Low and behold I was pregnant even though I was still breast-feeding, was 44, and with my history. I was in shock, ecstatic but in shock.

    That’s why I am doing research to find out your fertility is elevated after giving birth. Answers are hard to come by despite my hours of research online. This is the first that I’ve stumbled upon that begins to provide some potential evidence via linkages. however, I do wish those studies would extend their analysis to women over the age of 40 and under the age of 45 because then he becomes even more relevant since all of their quantitative data says that we are most likely at ver low fertility at this point even in the best of circumstances.

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