Fertility

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

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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Until 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, these women’s fecundability began to decline, and by 35, their fecundability was significantly lower than the average 20-year-old’s.

By contrast, the fecundability of women who had one or more births under their belts 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:

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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.

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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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6 replies »

  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!

  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

  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?

  4. Very interesting blog postings here. It is great to see actual science explained in a way that informs without talking down to people. I remember my mom, a nurse, telling me that she believed the reason that women who previously had a pregnancy were more likely to become pregnant more easily the next time was based on the anatomical difference between a cervix in a woman who did not have a previous vaginal birth (round opening) verses women who had (slit shaped opening), allowing easier ingress for the sperm. I was surprised to not see any discussion of this difference in anatomy and wondered whether you had come across any literature on this or not. Is there any data on pregnancy rates for women whose previous pregnancies were only c-sections verses vaginal deliveries, which could give some support to this theory? Also, is there any data on whether having more than one previous child changes the fertility rate compared to only one previous child? I’m curious as a mom of three, who is considering starting over in her 40s; each of my children were conceived in the first cycle we tried. I practiced the fertility awareness approach to increase odds of conception once we started trying, but with #1 we couldn’t even time things well with my husband being out of town on a week long trip, so he was conceived based on our activity five days prior to my ovulation based on BBT, CF and CP.

    Another possible topic I would suggest to you would be the odds of ovulating based on days off birth control pills. I did come across a couple of studies that delays in resuming the pill for the next cycle pack can lead to ovulation, but the risk is still slight even with an extra five days off the active pills, which I thought was interesting, because developing follicles will regress once the pill is restarted unless they have reached a sufficient size prior.

  5. Just a reminder that for many of us with serious “infertility” issues, having a single miracle child doesn’t reset anything. We still have the same diagnoses, and the same dire prognosis. BUT, because of these studies, our doctors are suddenly saying, “Well, you did have one before . . .” But, you know- I’ll take any up in chances I can get!

    I had an FSH of 34, undetectable AMH, tiny follicle count, endometriosis, and repeated chemicals and miscarriage. Doc said only way was donor eggs. I spent about 3 months doing ALL THE THINGS- diet, acupuncture, yoga, meditation, getting rid of toxins (e.g., phthalates, parabens, and other endocrine disruptors), and got pregnant naturally.

    My little boy is just over 2 years old now, and my numbers are all just as bad and I’ve had more chemicals and miscarriages. The only way I’m having another miracle is to do ALL THE THINGS again. But, now I know in my gut that my body can do it– and believing is half the battle!

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