I’m 32 weeks pregnant. At my 20 week ultrasound, they found that my placenta was low and near my cervix. I’ve got another ultrasound scheduled for next Wednesday to see if it has moved. I also had a low placenta with my previous pregnancy. It moved, although I had to have a C section in the end for other reasons. (I know I’m going to have to have one this time, too, regardless of what the placenta does) Last time my placenta was anterior (in the front), this time it is posterior (in the back). There was only one baby in my first pregnancy, and there’s only one in there now.
I’ve been reading about placenta previa online, of course. The sites I’ve read about placenta previa say it’s more common in mothers over 35. I was over 35 during my last pregnancy. But they don’t say why placenta previa would be more common in older mothers. I at least kinda-sorta understand why chromosome problems are more common in older mothers (though my biology background is quite minimal). I understand why having a larger placenta, as you might with twins, would make placenta previa more likely. I understand why things like C section scars might affect placenta previa, at least if the placenta in the second pregnancy was roughly in the same place as the first. I’m pretty sure that isn’t what’s happening with me, though- the first placenta was in the front, this one is in the back, so I’m pretty sure this one isn’t over the scar from the C section. Does anyone know why placenta previa is more common in older mothers?
The bottom line is that no one knows why placenta previa is more common among older moms.
I suppose the fact that PP is also more common among women who’ve had multiple pregnancies, raises at least one possibility, though. Specifically, the more pregnancies a woman has had, the fewer areas there will be remaining in the uterus of previously ‘unused’ (‘virgin’ ;)) sites for implantation of the egg.
In other words, if you assume that implantation tends to occur preferentially in areas remote from the cervix, and if you also assume that implantation tends to occur preferentially in previously ‘unused’ areas of the uterus, then the only spaces remaining for implantation in a woman who’s had multiple previous pregnancies will be close to the cervix.
What does that have to do with older women?
Even if an older woman has never had a baby, she may well have been pregnant before. I am referring not just to abortions (both therapeutic and spontaneous), but also to unrecognized miscarriages that occur very early in pregnancy (before the woman even knew she was pregnant). As I recall, even in recognized pregnancies, the miscarriage rate is around 20 percent, but in unrecognized pregnancies the rate is believed to be much higher than that.
More concisely, then, an older woman is more likely to have had previous pregnancies, especially unrecognized ones. As a result, she may have ‘used up’ the preferred, higher, sites for implantation and is thus more likely to have implantation occur lower in the uterus thereby setting the stage for placenta previa.
Just my WAG, mind you.