The Unbearable Uncertainty Of Biology

A new blood test could help make pregnancy more predictable, but uncertainty will always be with us.

AsianScientist (Jul. 27, 2018) – The path to parenthood is lined all the way through with uncertainty, so I often tell friends who are expecting to get comfortable with not knowing everything.

In line with that philosophy, I didn’t get all that excited after seeing the results of my home pregnancy test (the scientist in me said: could be a false positive), told my gynecologist not to tell me the sex of my fetus (why should it matter?), and opted not to do pre-natal screening (abortion wasn’t on the cards).

Despite my professed indifference to pregnancy-related information, there is one uncertainty-reducing test that I might consider if I were to be pregnant again in the future: this potential blood test for estimating gestational age and the likelihood of pre-term birth.

Nobody really knows your due date

If, for example, your doctor tells you that your expected due date (EDD, in mummy blogger parlance) is July 27, you can be 96 percent sure that your baby will not be born on that day.

Due dates are estimations arrived at by adding 280 days to the first day of your last menstrual period. This method is imprecise, to say the least, and assumes that (a) you have accurately remembered the date of your last menstrual period; (b) have a regular menstrual cycle of 28 days and; (c) conform to the ideals of a statistically ‘average’ person. So while due dates are undoubtedly useful for tracking the progress of your pregnancy, they aren’t terribly useful for planning when exactly you should start your maternity leave.

You might also be surprised to find out that ultrasound measurements don’t add that much more precision to your due date estimation. Your fetus’ age is typically estimated by measuring its crown to rump length, a measurement that is most accurate during the first trimester, with a margin of error anywhere between three days to two weeks. From the second trimester onwards, ultrasound-based estimates are even less accurate.

Why does it matter?

So if the baby will be born when it wants to be, why bother with the aforementioned blood test? For one thing, having an accurate due date estimation is crucial for evaluating how the fetus is developing and if there is any cause for concern. It also informs estimations of viability if the baby is born premature (a baby born at 26-27 weeks has a much higher chance of survival than a baby born at 24-25 weeks) and decisions on whether to induce labor or call for a Caesarean section.

The cell-free RNA test developed by Dr. Thuy Ngo and her colleagues at Stanford University may not be more accurate than an ultrasound, but it is much cheaper to perform and does not require expensive ultrasound equipment or trained personnel that are not routinely available in resource-poor settings.

The real benefit of the blood test, however, is that it not only provides an estimate of fetal age but can even be used to identify women at risk of preterm labor. According to the World Health Organization, some 15 million babies are born prematurely every year, often with no clear cause.

Despite significant advances in neonatal care, complications from premature birth remain the leading cause of death in under-fives, taking the lives of an estimated one million infants every year. Even when babies survive, they face the risk of lifelong intellectual and developmental disabilities. Knowing which pregnancies are most at risk could go a long way in informing would-be mothers to get help and reducing the health burden of preterm births.

Uncertainty reduced, not eliminated

That said, the blood test is nowhere near ready for consumer use. The pilot study was done on a small cohort of just 25 full-term and 13 preterm deliveries; it needs to be validated in larger, double-blinded trials before it can be safely used in the clinic.

Even as researchers continue working hard to reduce the uncertainties of pregnancy one non-invasive test at a time, it’s good to remember that the facts in biology are more statistical than deterministic. My advice at the start of the column still stands: science can help to reduce uncertainty but will never eliminate it; we’ve just got to learn to live with it.

This article is from a monthly column called From The Editor’s Desk(top). Click here to see the other articles in this series.


Copyright: Asian Scientist Magazine; Photo: Shutterstock.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Rebecca did her PhD at the National University of Singapore where she studied how macrophages integrate multiple signals from the toll-like receptor system. She was formerly the editor-in-chief of Asian Scientist Magazine.

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