Per Google research expert answer on babycentre:
platelets are cells in your blood that help your blood to clot when it needs to. The normal number of platelets is between 150 and 400 million per millilitre (ml) of blood. Most pregnant women have normal numbers of platelets, but about eight per cent of pregnant women have a slight drop in their platelet count. Your count is below normal if you have between 100 and 150 million platelets per ml of blood.
If your platelet count drops below normal while you're pregnant, it's called gestational thrombocytopenia. Gestational thrombocytopenia usually happens in the third trimester. It won't affect your baby, and your platelet levels will return to normal once your baby is born.
The reason you have a reduced platelet count is because you are pregnant. Experts are unsure exactly why it happens, but two factors may play a part:
Your body naturally destroys platelets if they are not used, and replaces them with new ones. In pregnancy, this process is speeded up. The result is that you have fewer, but younger and larger, platelets in your blood. Your body produces more of the liquid part of blood (plasma) while you're pregnant. This means that the platelets are more diluted, so are fewer in number per millilitre of blood. This doesn't affect how well the platelets work, though. They can still do their job.
Your blood test results should be written in your maternity notes. Your platelet count will look something like "Plat. 160x10.9/L", which means you have a platelet count of 160, which is in the normal range.
If your platelet count is low, the blood test should be done again. This will keep track of whether or not your count is dropping.
If your platelet count is extremely low, it may mean you're more likely to bleed either during or after birth, or during a caesarean section. Doctors may also be extra cautious about giving you an epidural. The epidural needle would have to be placed very carefully to avoid any accidental puncture.
It's hard to say how low your platelet count has to go before it becomes too low. This makes it difficult to tell at what point your risk of abnormal bleeding goes up. You should have extra tests if your platelet count falls below 100 million per ml of blood.
Occasionally, a very low platelet count could be a sign of a problem with your pregnancy. This could be a rare complication of pre-eclampsia, called HELLP syndrome, which also causes the following symptoms:
pre-eclampsia symptoms, such as high blood pressure and protein in your urine pain above your belly headaches nausea