Ready for more? Why birth spacing matters

“The World Health Organization and the American College of OB-GYNs recommend optimal pregnancy spacing somewhere in the range of waiting to conceive the next pregnancy at about 18 months up to about five years.”

Dr. Alison Gemmill, Assistant Professor, Johns Hopkins Bloomberg School of Public Health

Usually when we consider having another baby, personal preferences factor heavily into decisions around timing — things like budget or sibling dynamics. But it’s rare to consider the health impacts, and it’s even less common to discuss birth spacing with your doctor.

Jessica Rolph, your host, welcomes Dr. Alison Gemmill to today’s episode. Alison is an Assistant Professor at Johns Hopkins, in the Department of Population, Family, and Reproductive Health. She shares the biological benefits and risks associated with the timing of your pregnancies, with the goal of helping listeners make informed decisions about when to grow their families.


[1:35] What does the research tell us about the optimum time between pregnancies?

[2:27] What are the benefits of waiting 18 months between pregnancies?

[3:22] What should parents be doing about spacing between a miscarriage? 

[3:58] What about waiting more than five years?

[5:38] What risks are at play in the case of an older mom?

[8:51] What does research show in regard to the connection between autism and birth intervals less than 18 months?

[10:11] What is Dr. Gemmill’s theory on how much the baby takes from the mother’s nutritional reserve and for how long it takes to build that backup?

[11:33] Jessica shares her top three takeaways from her with Dr. Gemmill.


Jessica: Welcome, Alison.

Alison: Oh, thank you for having me. I’m excited to talk about this topic.

Birth spacing recommendations

Jessica: It’s so great to have your expertise here with us, so what does the research tell us about the optimum time between pregnancies?

Alison: Right now, we have recommendations from places like the World Health Organization and the American College of OB-GYN’s that does recommend optimal pregnancy spacing somewhere in the range of waiting to conceive the next pregnancy at about 18 months up to about five years. And so the World Health Organization specifically recommends that women wait until at least 18 months after birth, and then here in the US, we see strong recommendations to avoid inter-pregnancy interval shorter than six months because we know that those very short intervals are associated with negative outcomes.

Benefits of waiting 18 months 

Jessica: So what are the benefits of waiting 18 months between pregnancies.

Alison: So we have seen from many studies across many settings that in general pregnancies that are spaced between 18 months and up to five years, they tend to have better outcomes both for the mother and the baby, and we especially see this for outcomes like pre-term birth and low birth weight. And for moms, we see this potentially with complications that might arise, but one of the big considerations is that these relationships are not necessarily causal, and when we look at more rigorous study designs, it looks like there’s probably more… The risk factors for short inter-pregnancy intervals are really concentrated in that really short interval up to six months.

Jessica: And so what should we be doing about spacing between a miscarriage? 

Alison: That’s a really good question. So the guidelines that we were seeing from places like the World Health Organization didn’t really have any specific recommendations for people that had experienced miscarriage and even stillbirth more recently, we’ve seen studies so that indicate that really it doesn’t really matter how long you wait. So that’s good news, you don’t have to wait this recommended 18 months, for example, and that’s the same for stillbirth, like I said. So that’s good news.

Maternal age considerations

Jessica: And what about maternal age. So how do we think about… How do we think about the risks that grow when you are a little bit of an older mom, I had my last baby when I was 40, and I remember wondering about birth spacing and that competing with maybe I should just get pregnant quickly because I’m getting older.

Alison: Yeah, so I think this is a really interesting question. So first of all, I should say that the risks associated with these adverse outcomes, especially things like pre-term birth and low birth weight, first of all, it’s a really modest risk, second of all, it’s not clear, that it’s really causal, and then… I totally agree. We need to balance the risk that we do know occur with maternal age, especially advanced maternal age, so really it comes down to potentially balancing out the increased risk of these the short inter-pregnancy intervals with the known risks of advanced maternal age. And part of my research has shown that among women who start child-bearing after age 35, they do have short inter-pregnancy intervals, and those short inter-pregnancy intervals are more likely to be intended and planned. And what’s interesting about that is we know that pregnancy planning and intention are associated with good outcomes too, so it’s a little complicated when we introduce that factor in there too.

So I think if you’re in your late 30s and you just had your first birth and you’re considering when to have your next child, I wouldn’t put so much emphasis on this inter-pregnancy link, maybe I would avoid very short intervals. This is something I haven’t talked about, but we know that pregnancies that are conceived really right after birth, so within six months, those ones maybe there really is something going on there, and that makes sense from the perspective of wanting this physiological recovery. But I think by and large, the research suggests that it’s probably okay if you want to start attempting pregnancy after those six months… I will say one thing that we are starting to see though, is if you had a complication during your first birth or delivery, that maybe you wait a little bit longer, so for example, if you had a cesarean section, you might want to wait at least a year, if you had other types of complications, like placental abruption is a really serious one, you might want to wait a little longer for that as well, and that makes sense, we just want to make sure that your body is fully recovered from those types of complications.

Birth intervals and autism

Jessica: So some research shows a connection between autism and birth intervals less than 11 months, what is this research and what do you know about this connection? 

Alison: Yeah, so we’re starting to see, a lot more research looking at outcomes beyond birth, and Autism is a very important neurodevelopmental outcome that we care about, so this research does show that short inter-pregnant intervals, but also long inter-pregnancy intervals are associated with autism risk. So the risk again, is modest, and we’re not sure, again, if it’s a causal association, if… There are hypotheses that if it is a causal relationship, it might be due to maternal nutritional depletion. So if we were to intervene, in addition to making sure that you space your births adequately, whatever that means to you, you also want to make sure that, you are in good health before you conceive and are taking prenatal vitamins and eating a well-balanced diet.

Jessica: I have this theory that you just have all the nutritional reserves and then you give a lot of them to your baby, and some of them are macronutrients that you’re eating and micronutrients, but some of them are just based on your body’s reserves and what they’ve stored, what we’ve stored up over many years of eating the way that we’ve been eating and trying to take our vitamins, prenatal vitamins. What is your theory on how much the baby takes of that nutritional reserve and then how long… What’s your theory on how long it takes to build that back up? 

Alison: I’m not a nutrition expert, but I do think that we know other areas that really matter for adverse outcomes that we can easily intervene on. So these are things like smoking, and getting adequate sleep and maternal stress. I guess the thing is, is that outcomes like pre-term birth and low birth weight, they are what we call multi-factorial, so there’s several different things that can influence these outcomes, and I think we just have to make sure that we’re approaching pregnancy and preconception health from a well-rounded place, we want to make sure we’re not being too obsessive because that’s the other thing, we don’t want to stress ourselves out. Right. And I think a lot of mothers feel that they have to be absolutely perfect when they carry a pregnancy, but we want to make sure we’re not stressing ourself out, so take care of yourself, and I think… Do the best you can.

Jessica: That’s really helpful to hear because oftentimes, we do put so much pressure ourselves, but again, that pressure makes us stressed, so let’s just relax and enjoy the pregnancy. Alison, it’s been so wonderful having you here with us today.

Alison: Oh, thank you so much for having me. It’s been really fun to talk about.


Learning the science behind birth spacing has been an intention of mine for a long time! Here are my takeaways from the conversation with Dr. Gemmill.

  1. The World Health Organization recommends 18 months between pregnancies. In the US, the recommendation is to avoid intervals shorter than 6 months between births. Post miscarriage there is no recommended waiting period. 
  2. Outcomes like preterm birth and low birth weights are more common with a shorter interval between pregnancies, but Dr. Gemmill cautions that these risks are modest and the relationships are not necessarily causal. A variety of factors influence these adverse outcomes, so best to take a balanced approach. Make your sleep, prenatal supplements and a healthy diet a priority, and avoid stress to the extent possible. 
  3. Dr. Gemmill says older moms should avoid really short intervals (within 6 months) but can space their babies closer together to balance the risks that come with pregnancy after age 35. 

Pregnant with your second? Listen to My New Life Episode 22: “New additions: Bringing home a sibling” with Gabrielle Felman. And you’ll find more insights on sibling dynamics on the Lovevery blog


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