Science Questions

Is morning sickness inherited?

Sun, 8th Mar 2009

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Katherine Ryan asked:

Hi, I'm Katherine Ryan. I'm a stand-up comedienne who's pregnant and getting sick on the bus every day. I was just wondering who I can blame. Is morning sickness inherited?


Chris - I can probably help you out there. Yes, morning sickness is because by definition it's genetic. When you're pregnant you've got someone else's DNA in you and as a result it makes you get sick. Everyone gets it, pretty much, once or twice in your lifetime depending on how many times you get pregnant. Therefore you could say it is inherited. What actually is it? This is emesis gravidarum which is a fancy Latin expression which means 'puking of people who are pregnant.' Why this happens is we think it's down to a hormone called beta-hCG: human chorionic gonadotropin. This is a hormone which is produced by the early foetus, just as it's beginning to implant into the uterus. It puts this into the bloodstream to maintain the survival of a structure called the corpus luteum which is where the egg came from in the ovary. That structure makes progesterone. Progesterone keeps the uterus lush and well-supplied with blood so it can sustain a pregnancy. Until the placenta develops properly which is where the progesterone comes from afterwards you need that corpus luteum to stay alive. That's where you make beta-hCG. But it seems to mimic another hormone called TSH: thyroid stimulating hormone. When women are pregnant they seem to have a slightly higher metabolic rate. It might be that part of the symptoms are your metabolic rate going up because you have more active thyroxine, the body's own thermostatic hormone. As a result of that extra thyroxine level you are made to feel as if you are being sick more often. Usually though, it's not major problem., It comes on at 2 months of pregnancy, it peaks at 3 months and is gone by 3 or 4 months. There are some people who are very unfortunate and they have hyper-emesis and this can necessitate hospitalisation, unfortunately because it can be so severe. There is some evidence that can run in families but I think the numbers are so small there's not been any really strong, robust evidence to actually confirm that.


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