BY DR NORAFIDAH AHMAD
CONSULTANT OBSTETRICIAN AND GYNAECOLOGIST
KPJ SABAH SPECIALIST HOSPITAL KOTA KINABALU
Hypertension is also known as high blood pressure. It is a commonest medical problem encountered in pregnancy. Due to this, blood pressure is routinely assessed during each antenatal visit.
Blood pressure readings are recorded as two numbers. Systolic blood pressure is the higher reading. It measures the pressure in the blood vessel wall when the heart contracts. Normal readings of systolic blood pressure are about 120mmHg (millimetres of mercury). Diastolic blood pressure is the lower reading. It measures the pressure in the blood vessels when the heart relaxes between beats. Normal readings of diastolic blood pressure are about 80mmHg. When the blood pressure is consistently 140/90 or higher, hypertension is diagnosed. Severe hypertension occurs when the blood pressure is 160/110 mmHg or higher.
Hypertension complicates 10 to 15% of all pregnancies. Hypertension in pregnancy can be divided into pre-existing hypertension, pregnancy induced hypertension and pre-eclampsia. Pre-eclampsia affects 3 to 5 % of all pregnancies. Eclampsia occurs in approximately 1% of women with pre-eclampsia. It is a serious medical condition which is associated with convulsions and other complications such as stroke, kidney and liver failure.
Pre-existing hypertension is also known as chronic hypertension. In pre-existing hypertension, women are usually diagnosed as hypertensive prior to pregnancy. If hypertension is noted for the first time in the early pregnancy it is also likely that it is a chronic pre-existing problem. In this type of hypertension, the blood pressure will not return to normal after delivery.
Pregnancy induced hypertension is diagnosed when a woman’s blood pressure is normal before pregnancy but consistently rises to more than 140/90 mmHg after about 20 weeks of pregnancy. The blood pressure usually returns to normal after childbirth. However, some women may remain hypertensive following delivery and continue to develop chronic hypertension.
Pre-eclampsia is a condition where the maternal blood pressure is elevated in the second half of pregnancy along with presence of other signs and symptoms such as an abnormal level of protein in the urine and abnormal blood results. It is a potentially serious condition which can threaten the health of mother and baby.
Pre-eclampsia can also occur in women with pre-existing chronic hypertension. This carries a higher risk to mother and baby as compared to chronic hypertension alone. Regular monitoring is required to detect this superimposed pre-eclampsia condition.
In women with pregnancy induced hypertension and pre-existing hypertension, blood pressure must be regularly monitored. Treatment to lower blood pressure is important if blood pressure readings are consistently higher than normal. This is in order to avoid serious complications for mother and baby. However for mild to moderate hypertension, medication may or may not be recommended. Severe hypertension always requires prompt treatment to lower the blood pressure. There are a few types of anti-hypertensive medications which are available and safe to be used in pregnancy. Although some may cause side effects, they are usually well tolerated by most women. In some women, a combination of medications may be necessary to achieve good blood pressure control.
Pre-eclampsia affects one in every 10 pregnancies. Its severity varies from mild to severe. Pre-eclampsia can progress to eclampsia if left untreated or does not respond to treatment. Eclampsia
is a medical emergency and requires urgent multidisciplinary treatment to ensure safety of mother and baby.
The exact cause of pre-eclampsia remains unclear. It is most likely due to problems with the development of the placenta during the early stages of the pregnancy. Placenta is a tissue which carries oxygen and nutrients from the mother to the baby. Failure of implantation of placenta to the wall of the uterus causes baby at risk of not receiving oxygen and nutrients.
Although it is not possible to accurately predict the women who will develop pre-eclampsia, several risk factors such as general, genetic and medical factors are found to be associated with this condition. The risk factors includes teenage or advance maternal age, obesity, history of previous pregnancy with pre-eclampsia, women with a mother or sister with a history of pre-eclampsia, first pregnancy, twin or multiple pregnancy, long birth interval and some fetal chromosomal disorders. Woman with pre-existing medical conditions such as diabetes, kidney disease, chronic hypertension, autoimmune disorders and blood clotting disorders are also at risk of developing pre-eclampsia.
Pre-eclampsia usually occurs in the third trimester of pregnancy (28 weeks onwards) although in some women it may occur earlier. Women with pre-eclampsia are usually asymptomatic when the disease first occurs. They commonly present with elevated blood pressure and abnormal level of protein in the urine. Apart from that, they can also develop significant symptoms such as rapidly progressive swelling over hand, face and feet; visual disturbance; pain over upper abdomen; vomiting and headache.
If pre-eclampsia is diagnosed, admission to hospital is usually required. Blood pressure is monitored closely. High blood pressure may require oral or intravenous anti-hypertensive medications. Blood and urine tests are performed. Urine test will be able to quantify the level of protein in the urine. Blood tests are carried out to look for altered blood clotting, abnormal liver and kidney function. Monitoring of the baby’s well being can be done by assessing baby’s heart rate tracing, growth, blood flow in the umbilical cord and the amount of amniotic fluid.
The only cure for pre-eclampsia is delivery. However, if the pregnancy is less than 36 weeks, the decision to deliver will be based on the severity of the pre-eclampsia and the risk of prematurity. A major consideration in treating women with pre-eclampsia is to promote the baby’s growth for as long as possible in the uterus whilst keeping the mother’s risk under control. The delivery is however indicated if there is presence of any of the following conditions which are the inability to control maternal blood pressure; worsening general health and well being of the woman such as deterioration of kidney or liver function and reduction in blood platelet level which is important for proper blood clotting; presence of maternal symptoms such as severe headache, vomiting, visual disturbance and upper abdominal pain; baby not growing or showing signs of compromise; placental abruption (separation of placenta from the wall of the uterus) and if woman develop eclampsia.
If delivery is indicated in woman with pre-eclampsia, labour can be induced with medication to stimulate uterine contraction. The woman’s blood pressure is closely monitored throughout labour. High blood pressure will be given medication. If blood clotting is normal, epidural anaesthesia may be recommended. This is in order to relieve pain, lowers blood pressure and improve blood flow to the placenta. Baby’s well being is continuously assessed. If the baby is showing signs of distress, immediate delivery is necessary such as caesarean section.
If the pregnancy is less than 34 weeks, caesarean section is often recommended. This is because inducing labour can be difficult at early gestation and caesarean section is considered in the best interest of both mother and baby. In such cases, woman will usually receive steroid injections before delivery. This is to reduce risk of infant developing respiratory distress, bleeding into the brain and death after delivery.
After delivery, the mother needs to be closely monitored for at least the first 24 to 48 hours. The high blood pressure usually does not settle within first few days after delivery, so anti-hypertensive medication may need to be continued until blood pressure is stabilised. Blood pressure may take up to 3 months to return to normal. Woman should discuss with the doctor regarding risk or pre-eclampsia recurring in her next pregnancy and preventive measures.
Clinical studies have shown that a low dose of aspirin supplementation in early pregnancy may be able to reduce the risk of developing pre-eclampsia by about 15%. It should be started before 12 weeks gestation and continued throughout pregnancy. Apart from that, for women with a low calcium intake, supplementation with calcium during pregnancy may be able to reduce risk of pre-eclampsia.
If you have any enquiries relating to this topic, please do not hesitate to contact Dr. Norafidah Ahmad, Consultant Obstetrician and Gynaecologist at KPJ Sabah Specialist Hospital.