Is morning sickness inherited?

08 March 2009

Question

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?

Answer

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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