Blood pressure tends to decrease significantly and progressively during the first few months of pregnancy, to then stabilize and gradually rise to pre-pregnancy levels in the last trimester of gestation.
Despite the difficulties in establishing ideal reference values, the optimal diastolic level appears to be around 75 mmHg in the first and second quarters, and 85 mmHg in the last two to three months of pregnancy.
Responsible for this physiological drop in blood pressure is a set of factors, including the reduction of peripheral resistance (vasodilation), which prepares the body for an increase in blood volume, with an increase in glomerular filtration rate and cardiac output. The increase of this last parameter, which represents the quantity of blood expelled from the heart in a minute, is subordinated both to the increase in the heart rate and in the systolic range.
In pregnant women, much of the blood flow is located in the uterus-placental area, where nutrient, gas and waste substances are exchanged between the maternal and fetal blood, without there being direct contact between them. It is no coincidence that the placenta is richly vascularized and receives up to 10% of total maternal cardiac output (about 30 liters / hour). In order for these exchanges to occur, the pressure at the placental level must be low; we are therefore talking about a low-resistance deciduous organ (it does not significantly oppose the free flow of blood).
Predisposing factors for preeclampsia
- Nulliparity (risk> 6-8 times)
- Twin pregnancy (risk> 5 times)
- Diabetes
- Hydatidiform and fetal hydrops (risk> 10 times)
- Preeclampsia in previous pregnancies
- Chronic hypertension
- Extreme ages
Preeclampsia symptoms
Hypertension, tachycardia, respiratory rate changes
Headache, dizziness, buzzing, drowsiness, fever, hyperreflexia, diplopia, blurred vision, sudden blindness
Nausea, vomiting, epigastric pain, hepatomegaly, hematemesis
Proteinuria, edema, oliguria or anuria, hematuria, hemoglobinuria.
Unfortunately, it can happen that due to an anomalous development the placenta opposes an excessive resistance to the blood flow, inducing an increase of pressure upstream. In these cases we speak of systemic arterial hypertension induced by pregnancy, or simply of gestational hypertension. This condition is potentially dangerous for both the health of the mother and the fetus, so much that in extreme cases it can seriously endanger the lives of both. When after 20 weeks of pregnancy hypertension (≥ 140/90 mmHg) is accompanied by proteinuria (loss of protein with urine), doctors talk about preeclampsia, whose symptoms and predisposing factors are shown in the table.
The low levels of pressure that characterize the first two months of pregnancy expose the woman to a greater risk of dizziness and fainting, but also to varicose veins and varicose veins, and to a general sense of weakness. The risk of having to deal with these problems mainly affects women who are overweight or who, before pregnancy, were already suffering from certain disorders attributable to low pressure. Unlike gestational hypertension and preeclampsia, however, when the pressure in pregnancy is too low there is no need to worry, as it is a physiological condition (obviously within certain limits).
For all these reasons it is fundamental that during pregnancy the blood pressure values are monitored at every medical check-up, but also weekly by the pregnant woman herself, who will take care of noting the values immediately reporting any anomalies to the gynecologist.
