This year, as she progresses through her pregnancy, New Scientist reporter Linda Geddes has been penning an often amusing and always interesting first-person “Bumpology” column on “the science behind pregnancy.”
A couple of weeks ago, she looked into what the science says about whether it’s possible to use so-called “natural” methods right before or during conception to increase your chances of determining the gender of your baby.
The best known of these is the decades-old Shettles method, which claims that if you want a boy, you should have sex as close to the moment of ovulation as possible. The theory is that Y-chromosome-carrying (male) sperm are speedier, and thus more likely to reach the egg first.
If you want a girl, on the other hand, the Shettles method recommends shallow penetration during sex, supposedly because X-chromosome-carrying (female) sperm are more capable of surviving the more “hostile” environment near the vagina’s entrance.
Maybe those theories sound reasonable on paper, but they haven’t held up in studies, reports Geddes.
As one expert told her: “There’s no evidence that male and female sperm swim differently, and there’s no evidence that they survive differently.”
Stress and food
Geddes did find studies that have reported an association (not a cause-and-effect) between certain factors in parents’ lives and the gender of their offspring. Here are a couple of the studies she cites:
- Canadian researchers found that British women working in “low-stress” jobs (such as the arts and education) are more likely to have sons than women in “high-stress” jobs (such as construction and manufacturing). The effect was small: 54 percent of the low-stressed women in the study had sons compared to 47 percent of the high-stressed ones. (My problems with this study are many. Most notably, it determined stress levels by job category alone, and not by any kind of direct measurement of the women’s stress.)
- Another study found that consuming lots of calories — particularly at breakfast (!) — during the weeks and months leading up to conception increased the likelihood of having a son. Almost 60 percent of the women in the study who consumed cereal daily had sons compared with 45 percent of those who ate the stuff “rarely or never.” (Yes, that finding does seem odd, and, yes, the study has many limitations that could have skewed its results, including its small size [750 women] and its reliance on having the women self-report their diet.)
Before you change your job or your breakfast habits to up your chances of having a boy or a girl when you next get pregnant, let me emphasize again that such studies are observational. They shouldn’t be interpreted as showing that one thing (like eating lots of Cheerios) will cause another thing (a baby with a penis).
Which means, as Geddes herself points out, “None of this is much help for parents desperately hoping for a child of a particular sex.” Furthermore, she adds, “although some effects can be seen at the population level, the effects are small. We also don’t know how these different factors interact.”
In the end, in vitro fertilization is the only reliable way of determining the gender of your next child. Says Geddes’ expert: “At an individual level, you’ve just got to get on with it and be happy with what you’ve got.”
Note: Geddes has also delved into the science behind some of the old wives’ tales about predicting gender (such as bad morning sickness and/or weird food cravings means you’re having a boy) with some interesting results. You can read that Bumpology column here.