Birth Spacing… (Oh Yeah, We’re Pregnant Again.)

Yes, you read correctly, baby #2 is on the way… I have to say “baby #2”, rather than just “#2” because otherwise I keep having “WHO DOES NUMBER 2 WORK FOR?” on repeat in my brain. Sigh.

So our boy was born Aug 2013, and baby #2 is due late July 2015. Yep, your maths is correct, almost 2 years to the day. Cue barrage of “helpful” comments on birth spacing:

“Good you didn’t wait long, because you’re so old.”
“Less than two years? You’re going to die!”
“It’s great they’re close in age, they’ll be able to share.” (Kids and share? Ha!)
“At least you can just stay fat in between the kids and lose weight after.”
“So close together? Your uterus won’t recover.”

My fricken uterus?! What about my sleep patterns…? Wallet…? Sanity?

Anyway, there is a fair bit of information out there (mostly commentary) on ‘when you should have your next child’. Invariably there are articles from women who have had 4 kids in 5 years, and others who have gaps of up to 10 years between children, both claiming that their way is the way to go.

While things like how you feel about nappies, sleep patterns, and sibling rivalry are all very real issues to consider, for the purposes of this post I’m going to be concentrating mainly on the health/ medical aspects of birth spacing, or as it’s commonly referred to in the literature, interpregnancy interval (IPI).

Factors Affecting IPI

A shorter IPI is associated with:

  • The sex of the preceding child being female (true for some 55 countries). Yes, they ARE trying for a son… Even if they pretend that they’re not;
  • Countries with high infant mortality: shorter IPI means larger family sizes which (sadly) perhaps allows for the fact that some of their children don’t survive;
  • Both personal and community exposure to intimate partner violence;
  • Poor maternal health, including mental illness such as depression.

A longer IPI is associated with:

  • Breastfeeding;
  • Both knowledge about IPI, contraception AND access to effective contraception (with better outcomes if it’s publicly funded);
  • Unfortunately sometimes even when all these factors are present, a short IPI may result due to familial and societal pressures.

Effect of IPI – Baby

A short IPI is associated with low birth weight (V/SGA) and pre-term delivery/ birth.

  • One study found IPI <6 months associated with<200g reduction in birth weight, and 2x increase chance for SGA baby;
  • Another found IPI <6 months to be associated with pre-term delivery, (V)SGA, early neonatal death, and congenital malformations. The whole caboodle;
  • Interestingly it has been found that this relationship between short IPI and pre-term delivery is weak or non-existent with older mothers (age >35 years). Perhaps the higher powers are letting you pump out some babies without incident before your ovaries finally close up shop.

A short IPI is associated with greater neonatal morbidity and mortality.

  • Highest risks seems to be for IPI <6 months (but some studies find this risk extends all the way up to 5 years);
  • Some studies in South Asia have shown that more than 20% of infant deaths are attributable to short IPI (eg. In Bangladesh, India and Pakistan, one in 14 births ends with the child dying before 1 year of age. Truly tragic);
  • Children born within 18 months of their preceding sibling have double the risk of mortality (this risk of mortality extends into the early childhood years);
  • A child’s survival has been found to be much lower when born <1 year after their sibling; survival is highest when born ~5 years after.

A short IPI is associated with a greater chance of congenital anomalies / birth defects.

  • The risk of gastroschisis is higher in a child born <1 year after their sibling;
  • Conversely a long IPI (eg. >6 years) is also associated with adverse child outcomes – pre-term delivery, SGA, congenital anomalies;
  • IPI more than 8 years is a risk factor for shoulder dystocia (not a birth defect as such, but a complication at delivery).

A short IPI is associated with a greater risk of autism in the subsequent child.

  • A recent Californian study reported an increased risk of autistic disorder in children conceived within a year after the birth of a sibling;
  • A similar study in Norway found that there was an increased risk of autistic disorder in the second-born child after an IPI;
  • It has been suggested that micronutrient deficiencies (eg. Vitamin D) may explain this relationship…
  • HOWEVER, another study explains it differently: they suggest that bottle feeding (more likely with later children compared with first-born) brings an earlier return of fertility post pregnancy, with the resultant short IPI meaning a higher risk of your subsequent child having autism. They conclude that bottle feeding causes autism. A bold statement.

A short IPI is also associated with negative outcomes in the index (1st) child.

  • The adverse child outcomes aren’t only for the child born soon after their sibling; they exist also for the index child;
  • For instance, mothers who have a second child within 2 years of their first child are more likely to be neglectful of their first child, and their first child is more likely to have behavioural problems.

Effect of IPI – Mother

We’ve established that decreased gestation age and pre-term delivery is more common with short IPI.

  • One study looked at IPI and risk of preterm delivery while also considering maternal education levels (low maternal education levels are also associated with preterm delivery);
  • It found that increasing IPIs will have no effect on preterm delivery unless the problem of low maternal education is addressed as well.

Does short/ long IPI affect the mother’s cardiovascular health?

  • It has been postulated that short IPIs are associated with damaging the mother’s cardiovascular health (as a stressor from the metabolic changes of pregnancy);
  • Conversely, it is also thought that long IPIs may reflect subfertility, also associated with cardiovascular disease;
  • A recent study however has found that neither short nor long IPI is a risk factor for later cardiovascular health in the mother. Phew.

Relationship between Short IPI and Adverse Outcomes.

  • The current explanation for why short IPI results in adverse outcomes is long and varied;
  • It includes maternal nutritional depletion, folate depletion, cervical insufficiency, vertical transmission of infections, suboptimal lactation related to breastfeeding-pregnancy overlap, sibling competition, transmission of infectious diseases among siblings, incomplete healing of uterine scar from previous Caesarean delivery, and abnormal remodelling of endometrial blood vessels. Wow.

Other maternal factors affecting birth outcomes.

  • With all the studies mentioned so far, it is inferred that the short IPI (and related factors) is causing the adverse outcomes;
  • An Australian study looked at IPIs and their outcomes PER MOTHER (ie. for different pregnancies for the same woman);
  • Interestingly they found that within mother, there was a much weaker effect (compared with other studies) of short IPI on poor outcomes like pre-term birth and low birth weight;
  • This suggests that the apparent causal effect of short IPIs on adverse birth outcomes may be due to as yet unexplained maternal factors.

IPI Following Pregnancy Loss

Here the rules differ a bit…

  • Standard medical advice is usually to wait 3 months after a pregnancy loss before trying for pregnancy again (doctors usually say “after you’ve had a couple of normal cycles”);
  • One study found that live birth rates and adverse pregnancy outcomes (including further pregnancy loss) are not associated with short IPI after previous pregnancy loss (therefore the traditional recommendation may be hogwash – my word, not theirs);
  • Indeed another couple of studies looking at the effect of IPI on pregnancy outcomes after pregnancy loss found that IPI <6 months was associated with a lower rate of subsequent pregnancy loss. In other words, get back on the horse again early. The author of one such paper was called Dr Love… With a name like that you gotta trust him right?
  • Interestingly the same finding was not present for pregnancy following medical abortion/ termination (eg. With mifepristone). One study found an increased risk of SGA baby if pregnancy occurred <6 months after the termination.

IPI Following Uterine Instrumentation

Again, the rules are different…

  • Optimal IPIs may be different (likely longer) following Caesarean section (for obvious reasons, the main fear being one of uterine rupture);
  • One study found a much higher risk of uterine rupture with IPI <7 months after a previous Caesarean section;
  • This risk is obviously much higher if induction agents are given;
  • Just FYI, our obstetrician told us to wait 1 year after our emergency C-section before getting pregnant again. There you go, an anecdotal report 😉

Ideal IPI

Looking at the studies, there is no ‘ideal’ IPI – suggestions range anywhere from more than 6 months, all the way up to 5 years.

In terms of guidelines, what does the Big Boss (World Health Organisation) say about birth spacing/ optimal IPI?

  • Wait at least 2 years before attempting your next pregnancy (note ATTEMPTING, not actually being pregnant);
  • This is consistent with the literature discussing mother and baby risks, and also with the WHO/UNICEF recommendation for breastfeeding for at least 2 years;
  • The one exception to this rule is the gap after a miscarriage/ abortion: recommended wait is at least 6 months (but as we can see from the studies, there may be cause to review this recommendation in the future).

So? What does this mean?

  • For you – preferably don’t get pregnant again within 6 months, and don’t wait too long (>5-6 years);
  • For me – we fall under the recommended WHO time period of 2 years.

The studies have shown that there are a whole lot of factors to be considered when looking at the relationship between IPI and child/ maternal outcomes, therefore this is not something I’m going to lose sleep about. Besides which…

Study Limitations

  • Definitely worth a mention… There are lots!
  • Most of these studies rely on retrospective data (eg. Patient self-report) which is notoriously inaccurate and subject to bias;
  • Additionally different categorisations (eg. What constitutes a short or long IPI, different birth weights, different measures of adverse outcomes – eg. Disease screening scales, etc.) all make inter-study comparisons difficult.

Bottom line

  • ‘Official’ guidelines recommend waiting at least 2 years between children;
  • Both short and long IPIs have been shown to have adverse effects on child and maternal outcomes;
  • Current studies in the area of birth spacing/ IPIs have major flaws;
  • In the end (and I hate saying this because it sounds so blegh) you need to consider the evidence in the context of where you’re at, and what would work for you, and make your own decision 🙂

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