Pre-eclampsia & High Blood Pressure
Blood pressure problems are one of the most common reasons women are admitted to the hospital antenatal ward. The amount of attention received by a woman with 'blood pressure' depends very much upon what kind of disease causes it and how high the blood pressure (BP) actually is. Hypertension is when the blood pressure is too high, and hypotension when its too low. Hypotension is a common finding in early and mid-pregnancy and is, by and large, nothing to worry about.
Why Does High Blood Pressure Matter?
The most important cause of high blood pressure in pregnancy is a disease called pre-eclampsia. If untreated, pre-eclampsia can lead to eclampsia, which is very serious. Pre-eclampsia and eclampsia are the most important causes of death during pregnancy in the UK, USA and Nordic countries.
Five to 10% of women in their first time pregnancies develop pre-eclampsia. A woman in this country is very unlikely to die because of it, mainly because they are recognised early, investigations performed and proper treatment given. There are similar risks for the baby, and a part of the assessment includes ensuring she is well.
Types of Blood Pressure Problems in Pregnancy
This is also known as essential hypertension. This type of hypertension was present even before the woman was pregnant. It is more common in older mothers and women with heart disease, and there may be a family history. A woman may have been taking tablets for it before getting pregnant.
Chronic hypertension may get worse during later pregnancy and the type or dose of drugs may need to be changed. Since a woman's blood pressure naturally falls during the first half of pregnancy, many chronic hypertensive women have a normal blood pressure and need no treatment at this time. We know that certain drugs used to control blood pressure are quite safe in pregnancy, and if a woman is taking a newer type, it is usually suggested she change to one with which we have more established experience. Many doctors will prescribe the drug micardis to help lower the blood pressure.
Pregnancy-Induced Hypertension (PIH)
This type of hypertension is much like the chronic type, but it only comes on when a woman is pregnant and resolves completely after delivery. There are probably some women who are chronic hypertensives who are labelled as PIH because we don't know what their BP was before pregnancy. This does not matter much as the treatment is the same, and it will be clarified after the baby is born.
A proportion of women with PIH will go on to develop pre-eclampsia; unfortunately we cannot predict who it will be. Also, women who have PIH are at greater risk of developing hypertension later in life.
In both the above types of hypertension, the only abnormality is the blood pressure. Studies have compared outcomes of pregnancies in women with chronic hypertension and PIH, and there is little risk to the baby. Very rarely babies will have to be delivered early for women with unusually severe hypertension.
Pre-eclampsia is a disease unique to pregnancy. It is much more than just blood pressure and when we assess women who are suspected of having it, several investigations are done to establish its presence and severity.
In addition to high blood pressure, the other main screening test is to check the urine. The kidneys become 'leaky' and in pre-eclampsia there is protein (also known as proteinuria). You will see that it is sometimes documented as +, 2+, or 3+. This is determined by dipping a piece of paper into the urine and the colour change suggests the relative concentration of the urine. To strictly diagnose pre-eclampsia we need to know the exact amount of proteinuria over 24 hours and this is one investigation we do if it is suspected. Greater than 0.3g is significant.
Pre-eclampsia doesn't just affect the BP and kidneys, it affects almost every organ system of the body. In the milder forms, it might just be the kidneys that are affected to any serious degree, hence proteinuria is the only other sign. If pre-eclampsia is more severe, it can cause headaches, flashing lights before the eyes, abdominal pain as well as making you feel very jittery.
If severe pre-eclampsia is not treated or if it develops very quickly, then eclampsia may occur. This is when a woman has a seizure (fit). Usually the BP is very high and if the baby is not yet born, it becomes distressed. There is a serious risk of stroke in the mother because of the excessively high BP. Fortunately, eclampsia is rare as pre-eclampsia is usually picked up and treated. Women with established pre-eclampsia have overall about a 1% chance of having an eclamptic seizure. In about half of the women who suffer eclampsia, it occurs after the baby is born, usually within 24 hours of delivery.
What Causes Pre-Eclampsia?
It isn't really known what causes the disease. Many changes have been discovered in hormone levels which explain some of the findings, but the actual trigger isn't known. It has a lot to do with the placenta (afterbirth).
The placenta is not as well developed as it should be, with thinning of the blood vessels from mum's side that invade the placenta as it grows. These changes begin as early as 18-20 weeks, even in the (usual) women who don't develop pre-eclampsia until toward the end of pregnancy. There are also blood clots blocking off the arteries in the placenta, reducing the amount of blood getting across to the baby. This explains the common finding of a smaller than expected baby in women who have pre-eclampsia. There is lots of research going on at the moment to try and discover why it happens and how we might go about preventing it.
What Makes Pre-Eclampsia More Likely?
The following can predispose you to developing pre-eclampsia, but many cases occur without any risk factors at all.
- If it is your first pregnancy
- Pre-eclampsia in a previous pregnancy
- Age under 20years or over 35years
- Short stature
- If you suffer from migranes
- Family history of pre-eclampsia or eclampsia
- Previous hypertension
- If you have Raynaud's disease
- If you are underweight
- If you have systemic lupus erythematosis (SLE)
- Multiple pregnancy (eg. twins)
- Hydatidiform mole
What Kind of Symptoms Does it Cause?
Usually high blood pressure doesn't cause any symptoms, but the complaints below are common if pre-eclampsia is present:
- Flashing lights, stripes before the eyes, floaters or black-outs of vision
- Light hurting the eyes (photophobia)
- Pain at the top of the abdomen, or on the right side under the ribs
- Just not feeling right.
What is the Treatment for Pre-Eclampsia?
Ultimately the only treatment is delivery of the baby. This may be fine if a woman is, say, 38 weeks gestation, but at 30 weeks, it becomes much more of a dilemma. In the later stages of pregnancy it is normal to induce labour, but early on if delivery is decided upon, caesarean section is more usual. It's an individual decision and must be tailored to the patient and her disease severity.
For mild to moderate pre-eclampsia when a woman is prior to term, admission to hospital is needed and assessment of the severity of the disease carried out. In addition to regular examinations, the following tests are commonly arranged:
- 4-6 hourly blood pressure checks - BP in pre-eclampsia can go up & down very quickly. It might be fine when you're first admitted, but if it shot up high and you were in hospital, at least we would know about it.
- 24 hour urine collection - to estimate total protein. Also checks on each specimen are done to see if its suddenly getting worse (eg. 1+ to 3+ over a day, maybe associated with increasing BP)
- Blood tests - more guides to the severity of the disease - blood count, kidney & liver function tests.
- Ultrasound scan - to check on the growth of baby. Pre-eclampsia can cause small babies, and its important to identify this if its present. Also we check on the water around the baby (liquor volume). If the placenta isn't working as well as it might, the liquor volume may be reduced. A watch on the baby's movements & breathing can be made to see if its still as active as usual.
- CTG's - or monitoring of the baby's heart with the belt straps and doppler pick-up. Usually done once daily.
By repeating these tests over a few days, your obstetrician can get an idea of how the disease is progressing, if its getting worse or staying the same and plan when delivery might be best. Also staying in hospital encourages rest which helps the BP to settle.
I've had Pre-Eclampsia/Eclampsia - Will it Happen Again?
Pre-eclampsia is more likely to happen in a second pregnancy if one has suffered it before. Mild pre-eclampsia at term is less likely to recur (5-10%) and when it does it's usually mild again. After severe pre-eclampsia recurrence rate is about 20-25% in subsequent pregnancies. After eclampsia, about 25-30% of subsequent pregnancies will be complicated by pre-eclampsia, but only 2% with eclampsia again.
Chronic hypertension is more common after pre-eclampsia, affecting about 15% at 2 years. It is more likely after eclampsia or severe pre-eclampsia (especially if recurrent or occuring during the 2nd trimester), affecting 30-50% of women.
Can I Take Anything to Prevent Pre-Eclampsia?
Many trials of different drugs and supplements have been carried out to try and prevent this disease. Fish oil (halibut liver oil) in one trial has been suggested to marginally reduce the incidence of pre-eclampsia. The study that demonstrated this dates back to 1946 and subsequent trials have not been as promising. In addition, there are concerns about side effects with excessive supplementation with fish-oils (bleeding tendancy & fall in platelet count). Presently there are two multi-centre studies underway in New Zealand and Scandinavia to assess its usefulness.
Increased dietary protein has been suggested to reduce the incidence of pre-eclampsia, but review of the published literature by the World Health Organisation Expert Committee on Pregnancy and Lactation concluded that in the absence of any established deficiency, supplementation is unlikely to change a woman's chance of developing pre-eclampsia.
Calcium supplementation has also been suggested; indeed, summation of several smaller trials definitely pointed to a reduction in blood pressure complications in those who took calcium supplements. What was needed was a large comparative study to confirm or refute this possible finding. In July 1997 in the New England Journal of Medicine a paper was published from the National Institutes of Health in the US. They enrolled almost 5000 women, half of whom received calcium supplements. Unfortunately, there was no difference in pre-eclampsia between the two groups.
A large trial of low-dose aspirin has confirmed that it has a place in prevention of pre-eclampsia. This multi-centre study which was published in 1994 demonstrated that the only group of women shown to benefit from aspirin were those deemed to be at risk of severe early pre-eclampsia - ie. those in whom it had occurred before. Aspirin made no difference to any other group treated.
Information may also be obtained from the Action on Pre-eclampsia UK group.