Due Date

(Image via Wikipedia: Views of a Foetus in the Womb, c. 1510 – 1512, a drawing by Leonardo da Vinci.)

I will admit to occasional single-minded ranting. You might think that, as an astronomer who studies the outer part of the solar system, my rants are restricted to issues like classification of planets, bad weather at telescopes, and the possible effects of secular perturbation on the perihelion evolution of detached Kuiper belt objects. But my other main job, being a parent to a now-5-year-old daughter, provides me a plethora of new things to rant about, also.

My daughter provided me the very first opportunity before she was even born. Back then, she was code-named Petunia, and all I really wanted was some way to understand what Petunia's July 11th due date actually meant. The ranting really didn't begin until sometime in the third trimester. Here is an excerpt from How I Killed Pluto and How It Had It Coming from the moment when simmering frustration turns into full-scale rant.

Petunia was getting bigger. Her bones were hardening. Her eyebrows were growing. She had a July 11th due date, and, though there was not much I could do to influence anything, I could, nonetheless obsess about what, precisely, a due date means. I asked anyone who I thought might have some insight. I know, for example, that due dates are simply calculated by adding 40 weeks to the start of the mother's last menstrual cycle. But how effective is that? How many babies are born on their due dates?

Our child birthing class teacher: "Oh only 5% of babies are actually born on their due dates."

Me: So are half born before, half after?

Teacher: "Oh you can't know when the baby is going to come."

Me: I get it. I just want to know the statistics.

Teacher: "The baby will come when it is ready."

I asked on obstetrician.

Doctor: "The due date is just an estimate. There is no way of knowing when the baby will come."

Me: But of your patients, what fraction delivers before and what fraction deliver after the due date?

Doctor: "I try not to think of it that way."

I propose a simple experiment for anyone who works in the field of childbirth. Here's all you have to do. Spend a month in a hospital. Every time a child is born, ask the mother what the original due date was. Determine how many days early or late each child is. Plot these dates on a piece of graph paper. Draw a straight line for the bottom horizontal axis. Label the middle of the axis zero. Each grid point to the left is then the number of days early. Each grid point to the right is the number of days late. Count how many children were born on their precise due dates. Count up that number of points on the vertical axis of your graph and mark the spot at zero.

Do the same with the number of children born one day late. Two days late. Three. Four. Keep going.

Now do the early kids.

When you have finished plotting all of the due dates label the top of the plot "The distribution of baby delivery dates compared to their due date."

Make a copy. Send it to me in the mail.

My guess is that you will have something that looks like a standard bell curve. I would hope that the bell would be more or less centered at zero. It would either be tall and skinny – most kids are born within a few days of their due dates – or short and fat – there is quite a wide range around the due date.

One thing I know, though, is that the bell would have a dent on the right side. At least around here, no kids are born more than a week or two after their due dates. Everyone is induced by then.

I am usually capable of allowing myself to give up in trying to get the world to see things in my scientific, statistical, mathematical way. But this one mattered to me. If I were at a dinner party with Diane and the subject of due dates was ever breached Diane would turn to me with a slightly mortified look in her eyes and whisper "Please?"

I would rant about doctors. About teachers. About lack of curiosity and dearth of scientific insight and fear of math. I would speculate on the bell curve and how fat or skinny it was and how much it was modified by induction and C-sections and whether different hospitals had different distributions.

Inevitably the people at the dinner parties would be friends from Caltech. Most had kids. Most of the fathers were scientists. Most of the mothers were not. (Even today things remain frighteningly skewed, though, interestingly, most of my graduate students in recent years have been female. Times have no choice but to change.)

As soon as I started my rant the fathers would all join in: "Yeah! I could never get that question answered either," and they would bring up obscure statistical points of their own.

The mothers would all roll their eyes, lean in towards Diane, and whisper "I am SO sorry. I know just how you feel" and inquire as to how she was feeling and sleeping and how Petunia kicked and squirmed (as an aside, my female graduate students wanted to know the answer to my question, too, and were prepared to rant alongside me. Times have no choice but to change.)