Ask Dr Gary: More born in the light of day

Many years ago my mother observed that babies are mostly born from late afternoon until early morning, which is the time that most couples are enjoying each other the most. In my case, my own daughter was born, through the birth canal, to the minute she was conceived. Has anyone researched this? - J.B.

Let's approach these ideas one at a time. Sperm take anywhere from 30 minutes to five days to reach the egg and fertilise it, so the timing of intercourse and the timing of conception are only loosely related. If the timing of intercourse and the timing of the child's delivery are the same, down to the minute, it's pretty safe to consider it a coincidence. A baby is born in New Zealand roughly every nine minutes, so there are lots of opportunities for such a coincidence to arise.

Regarding intercourse, the studies show there's not as much variety as you may think. In the modern working world, 60 per cent of intercourse occurs at bedtime, and 30 per cent upon awakening. This is different to childbirth, which traditionally was observed as occurring mostly at night, and more specifically, in the early morning hours. There's a plausible explanation for this, as most other primates also give birth under the cover of darkness, when the risk of predators is less. Humans show this tendency, too, just less strongly than other primates.

But an interesting study this year from Spain showed that most modern births now occur during daytime. This is because of the many "unnatural" deliveries that are now commonplace, such as Caesarian sections and induced labours. Pregnant women with health problems such as smoking, obesity, medication use, or who are over 35 are no longer a rarity. With higher-risk pregnancies come higher-risk (and more medicalised) births. Consequently, many more of our children's births are scheduled to occur during the day, when obstetric and midwife staffing is more robust.