By Allen J. Wilcox
On making boy babies, and other pregnancy myths
In her novel, Prodigal Summer, Barbara Kingsolver celebrates the lush fecundity of nature. The main character marvels at the way her ovulation dependably comes with the full moon.
It’s a poetic image – but is there any evidence for it?
Actually, no. It’s true that the length of the average menstrual cycle is close to the length of the lunar cycle. But like so many notions about fertility, an effect of the moon on ovulation is just a nice story. The menstrual cycle is remarkably variable, even among women who say their cycles are “regular.” This is not surprising – unlike the movement of stars and planets, biology is full of variation. The day of ovulation is unpredictable, and there is no evidence (even in remote tribal cultures) that ovulation is related to phases of the moon or other outside events.
We humans are susceptible to myths about our fertility and pregnancy. These myths also invade science. One scientific “fact” you may have heard is that women who live in close quarters synchronize their menstrual cycles. The paper that launched this idea was published forty years ago in the prestigious journal Nature1. Efforts to replicate those findings have been wobbly at best – but the idea still persists.
Another scientific myth is the notion that sperm carrying the Y male chromosome swim faster than sperm carrying the X female chromosome. It’s true that the Y chromosome is smaller than the X. But there is no evidence that this very small addition of genetic cargo slows down the X-carrying sperm. As often as this idea is debunked, it continues to appear in scientific literature – and especially the literature suggesting that couples can tilt the odds towards having a baby of a particular sex.
Choosing your baby’s sex
Many couples have a definite preference for the sex of their baby. The baby’s sex is established at conception, which has led to a lot of advice on things to do around the time of conception to favor one sex or the other. Recommendations include advice on timing of sex in relation to ovulation, position during sex, frequency of sex, foods to eat or avoid, etc. The good thing about every one of these techniques is that they work 50% of the time. (This is good enough to produce many sincere on-line testimonials.) Despite what you may read, there is no scientific evidence that any of these methods improves your chances for one sex or the other, even slightly. The solution? Relax and enjoy what you get.
When will the baby arrive?
Everyone knows that pregnancies last nine months – but do they? Doctors routinely assign pregnant women a “due-date,” estimated from the day of her last menstrual period before getting pregnant. The due-date is set at 40 weeks after the last menstrual period. You might think the due-date is based on scientific evidence, but in fact, 40 weeks was proposed in 1709 for a rather flaky reason: since the average menstrual period is four weeks, it seemed “harmonious” for pregnancy to last the equivalent of ten menstrual cycles.
So what are a woman’s chances of actually delivering on her due date? Fifty percent? Twenty percent?
Try four percent. Just like the length of menstrual cycles (and every other aspect of human biology), there is lots of variation in the natural length of pregnancy. If the due-date is useful at all, it is as the median length of pregnancy – in other words, about half of women will deliver before their due-date, and about half after. So don’t cancel your appointments on the due-date just because you think it’s The Day – there’s a 96% chance the baby will arrive some other time.
1. McClintock MK. Menstrual synchorony and suppression.
By Dr Sesh Kamal Sunkara
In vitro fertilization (IVF) involves the retrieval of an egg and fertilization with sperm in the laboratory (in vitro) as opposed to the process happening within the human body (in vivo), with a natural conception. IVF was first introduced to overcome tubal factor infertility but has since been used to alleviate all types of infertility and nearly four million babies have been born worldwide as a result of assisted reproductive technology.
The birth of Louise Brown in 1978, the world’s first IVF baby was from a natural menstrual cycle without the use of any stimulation drugs. As success rates were low with natural cycles in the early days of IVF, ovarian stimulation regimens were introduced into IVF to maximize success rates. The aim was to retrieve more eggs to overcome the attrition in numbers at fertilization, cleavage, and implantation. However, with the introduction of ovarian stimulation regimens the complication of ovarian hyperstimulation syndrome (OHSS) arose.
There have been several discussions among IVF clinicians on what the ideal number of eggs should be to optimize IVF outcome and minimize risk of OHSS. We analysed a large database of over 400, 000 cycles provided by the Human Fertilisation and Embryology Authority (HFEA) in order to establish the association between egg number and live birth rate in IVF.
We found that live birth rate increased with increasing number of eggs retrieved up to 15 eggs and plateaued from 15 to 20 eggs with a decline in live birth rate beyond 20. The analysis of the data suggested that around 15 eggs may be the optimal number to aim for in a fresh IVF cycle in order to maximize treatment success whilst minimizing the risk of OHSS. We also established a nomogram which is the first of its kind that allows prediction of live birth for a given egg number and female age group. This is potentially valuable for patients and clinicians in planning IVF treatment protocols and counselling regarding the prognosis for a live birth occurrence, especially in women with either predicted or a previous poor ovarian response.
The full paper and supplementary data has been made publicly available here, as published in Human Reproduction by Sesh Kamal Sunkara, Vivian Rittenberg, Nick Raine-Fenning, Siladitya Bhattacharya, Javier Zamora and Arri Coomarasamy. Above table appears with full permission from Human Reproduction and Oxford Journals.
It’s being said that if you want a baby born on 11-11-11, you should “get ready to get on it this weekend.” So…
By Allen J. Wilcox
You already know where babies come from – the business about sperm and eggs, and getting them together. You also know something about birth control – after all, people spend most of their reproductive years trying NOT to get pregnant.
But there comes a time for many women when they ready to have a baby. That’s when some interesting questions arise.
- Once you stop using birth control, how long does it take to get pregnant?
- Is there something women should do to increase their chances of getting pregnant?
- What can a woman do to help make sure her baby will be healthy?
Let’s start with the last question first. The most important thing a woman can do before getting pregnant is to start taking daily multivitamins with folic acid. Folic acid helps prevent serious birth defects of the brain and spine (neural tube defects) and probably other defects as well. These defects happen very early in the baby’s development – waiting until you think you are pregnant can be too late.
Another thing you can do, if you are a smoker, is to quit smoking. Smoking puts a damper on women’s fertility (although apparently not on the fertility of men – life is not fair). Smoking also increases the small chance of fetal death later in pregnancy. Do yourself (and your baby) a favor, and give up the cigarettes.
Besides that, what should you do (besides the obvious)?
Nothing.
Really, nothing. You already have a lot going for you. Consider the benefits of your family history – not a single one of your ancestors was infertile. If you are a reasonably healthy person with no history of reproductive problems, and if you are having unprotected sex at least weekly, biology is on your side.
Some useful facts
There is a spectrum of fertility, ranging from very low to very high. You won’t know where you are on that spectrum until you actually try to conceive. On average, your chance of getting pregnant in the first month is 25%. For a few unlucky couples, the chances are zero – they are sterile. Other couples may have a 50% or 75% chance of getting pregnant in their very first month of trying. For couples as a whole, about half will be pregnant after three months. That goes up to two-thirds of couples after six months, and more than 90% after a year. Even if you don’t conceive in the first year, you still have a 50% chance in the next year or so. Only about 5% or so of couples are unable to conceive at all by natural means.
Probably the biggest predictor of fertility is woman’s age. Women are at their reproductive peak during their twenties. As they move through their thirties, their fertility begins to decline. This is relevant because many women (for lots of good reasons) delay their childbearing until they are in their 30s or even older. If a woman is not so fertile to start with, this delay can cause problems. Unfortunately, there is no medical test to tell women in advance how fertile they are.
The fertility window
Let’s get down to the biology. Pregnancy happens when couples have sex during the five days before ovulation and the day of ovulation itself. (In other words, sperm can survive up to five days in the woman’s reproductive tract.) This six-day fertility window gives you a fairly wide span of days in each cycle for intercourse that can produce pregnancy.
But there is a catch. Most women don’t know
