Studies of biological rhythms used to be very popular. A quick check on Medline showed me that in 1964-1973, 2/10 000 publications were related to biorhythm studies and in 2001-2010 there were more – 8/10 000. The spectrum of publications is slowly changing in the collection reflected in Medline, but the number of studies of biorhythms is at least not decreasing. This is bad news for me as I do not actively do research in this field now.

But 30 years ago I did, and one of my findings showed a weekly rhythm of arterial blood pressure in healthy air force pilots — a good example of the powerful social forces changing the functioning of the human body. Young males tend to drink alcohol, but they do it during the weekends.

Recently Alexander Saversky drew my attention to the weekly rhythm of deliveries in Russia (see a summary of the national statistic prepared by A. Saversky here - 
http://sites.google.com/site/vvvlas/professionallinks/-week-deliveries-russia). On week days an additional 150 000 children are born each day, compared with about 450 000 daily during Saturday and Sunday.

Of course, all planned induced deliveries tend to be scheduled for working days. And because caesarean deliveries are common (up to 50-60% of deliveries in some hospitals, as shown in the study by Kirill Danishevsky), they also tend to be delayed until weekday working hours.

But what is special for Russia is the high rate of hospital admissions of pregnant women. In some regions of Russia almost every pregnant woman is admitted to hospital for “medical indications.” There are two main reasons for this.
Firstly, despite a fall in the birth rate since the 1980s the number of beds in obstetric hospitals has not been reduced. Instead beds were transformed from “delivery beds” to “pathology of pregnancy beds.” Of course, the beds need to be filled.

Secondly, women tend to build up a relationship with their obstetricians so that they can feel reassured in case something goes wrong at the moment of delivery. Obstetricians in Russia offer a personalised service of their own in hospitals, and accept cash from families. Good doctors invite the pregnant woman to the hospital a couple of days before the prospective delivery, and after some days of waiting offer a caesarean section or induced labor. Naturally this is scheduled to happen during the working week. Most of these cases are registered as normal delivery, because the induction is done using the Cytotec (misoprostol) tablets, readily available in drug stores for $3 per box of 10.
We know about this practice not only from personal stories, but also from occasional reports of uterine rupture owing to overstimulation. What we do not know is what the health consequences of this practice are. It would be interesting to know whether somebody has looked at the outcomes of deliveries during working days compared with weekends.

Vasiliy Vlassov is a Professor of medicine at the Higher School of Economics, Moscow. His research interests are in epidemiology, evaluation of diagnostic tests, public health, and especially health care delivery with scarce resources. He is the co-founder and current president of the Russian Society for Evidence Based Medicine.