‘No man knoweth the hour’: The biblical case for ditching due dates

Only five per cent of births occur on their predicted date. After watching his wife struggle with the unreliability of due dates, Jack Chisnall wonders if it’s time to ditch them. Acknowledging our lack of abililty to control timings is biblical, he says 

“When are you due?”  

It’s a standard question for a lady with a bump. In the case of our most recent child, my wife and I would answer, beaming: “St Paddy’s Day”. The questioner might remark that was a good day to be born, or that the date is their mother’s birthday - or something along those lines. All-in-all, the conversation would confirm that humans feel that such date predictions are meaningful - and largely accurate.  

And yet, just five per cent of women actually give birth on the due date given to them by doctors. It does not even necessarily give a good ballpark: according to a 2015 review, about two-thirds will give birth within eleven days of their due date. The rest fall outside that fairly wide span. Given how many factors can be at play when it comes to gestation, it makes sense. A recent study found pregnancy lengths could differ by over a month - and that doesn’t include babies born preterm. 

A definitive due day is also a relatively recent thing, too. The method of counting a week from a woman’s last menstrual period (the LMP) was the brainchild of a Dutch doctor in the mid-18th century and, until ultrasound arrived, was the best we had. But even ultrasound has a margin of error. Its predictions are based on the size of the foetus against a standard. Big babies can be assumed to be older than they are; while small ones, younger.