High Blood Pressure and Pregnancy
High blood pressure and pregnancy can be a dangerous combination. If you have high blood pressure and are thinking about getting pregnant, make sure you check in with your doctor. You’ll want to do everything possible to keep you and baby safe.
High Blood Pressure Is Dangerous
High blood pressure is a problem even when you’re not pregnant. If not treated, it increases your risk of heart attack and stroke. It can also cause problems with your kidneys and your vision.
High blood pressure won’t usually affect your ability to conceive. However, once you become pregnant, high blood pressure brings a new set of risks. It can reduce the blood flow to the placenta. The placenta is the baby’s connection to your own body, allowing oxygen and nutrients to pass from you to him/her. Without proper blood flow, the placenta doesn’t work right and your baby can’t grow properly.
Another risk from high blood pressure is placental abruption. Normally, the placenta is attached to the wall of your uterus until the baby is born. If it detaches too early, which is called “abruption”, you can have severe bleeding into the uterus. This is dangerous for both you and the baby.
High blood pressure can also increase the chance of your baby being premature.
Treating High Blood Pressure in Pregnancy
If you normally control your high blood pressure with diet and exercise, following the same routine may be all you need to do. Check with your doctor to find out if your exercises are safe for the baby, or if there’s a time in pregnancy when you should stop.
Some blood pressure medications are considered safe to use during pregnancy, but some are not. If your high blood pressure is mild, your doctor may have you stop taking medicine altogether. Most women experience a drop in blood pressure during the first half of pregnancy. It’s possible that your blood pressure will be normal during that time. Later on, close monitoring will help you know if treatment is needed.
Doctors don’t know if any blood pressure medicines are 100% safe during pregnancy, but some are safer than others. For example:
- Methyldopa: (Brand name Aldomet) This drug is often used for the combination of chronic high blood pressure and pregnancy. The FDA rates it as “usually safe” in pregnancy. Side effects include dry mouth and sleepiness. Serious adverse effects include liver problems.
- Pindolol: (Brand name Visken) This medicine is a type of beta-blocker. Many beta-blockers are not used in pregnancy because they are thought to cause mild fetal growth restriction. Pindolol seems to have a lower risk of causing this problem, although doctors can’t say for sure. It’s also rated “usually safe” by the FDA.
- Nifedipine: (Brand names Adalat and Procardia) This is a type of calcium channel blocker. The FDA says that “safety during pregnancy has not been established,” which simply means that it hasn’t been thoroughly studied. Many doctors feel that it’s safe; your own doctor can help you make the decision.
- Angiotensin-converting enzyme (ACE) inhibitors: (Brand names Vasotec, Prinivil, and Altace) ACE inhibitors should not be used during pregnancy. They can cause the baby’s kidneys to develop improperly and even lead to fetal death. Angiotensin II receptor blockers are another type of medicine that work in a similar way. They should be avoided during pregnancy, too.
Early in your pregnancy, your doctor will do some routine tests to check for anemia and other problems. For women with high blood pressure, these tests should always include a urine test for protein and a blood test for liver function. This is because preeclampsia, a dangerous condition that can develop during pregnancy, involves high blood pressure, protein in the urine, and sometimes liver problems. The high blood pressure in preeclampsia has a different cause than chronic high blood pressure, and it can signal immediate danger.
If your blood pressure goes up during your pregnancy, your doctor will need to know if it’s just your usual high blood pressure or a sign of preeclampsia. Comparing new tests to your baseline values will help.
More Information About High Blood Pressure and Pregnancy
To learn more about chronic high blood pressure and pregnancy, try these sites:
Rhesus factor and pregnancy
Not everyone's blood is the same. Blood is classified into groups, the most well-known being the ABO system in which a person’s blood is recorded as either A, B, AB or O, depending on the types of chemicals identified in their red blood cells. When someone needs a blood transfusion it is important that they are transfused with blood from the same group as their own. Otherwise a reaction to the ‘foreign’ blood may occur.
The rhesus factor
Each blood type is also further identified by a plus or minus sign after the letter of the alphabet. For example, someone's blood may be ‘O positive’ (written O+) and another ‘AB negative’ (written AB-).
The plus or minus sign refers to the presence or absence of a substance in blood known as the rhesus factor, so named because it was first discovered in rhesus monkeys.
Most people are rhesus positive (Rh+). But if a rhesus negative (Rh-) person receives Rh positive blood, their body reacts, making chemicals (antibodies) to defend against the foreign rhesus factor. This is similar to the way we make antibodies to various viruses such as rubella (German measles) and chickenpox.
The rhesus factor and pregnancy
During pregnancy, or at birth when the placenta comes away from the wall of the uterus, some blood cells from the baby’s circulation sometimes make their way into the mother’s bloodstream.
This is normal and for most women not a problem. However, it becomes significant for women who have Rh negative blood. If the baby has Rh positive blood inherited from the father, and the mother and baby’s blood cells become mixed during gestation or delivery, the mother’s body may treat the baby’s blood cells as foreign substances and produce antibodies against them (Rh antibodies).
This doesn’t often cause problems during a first pregnancy, because there’s usually no significant contact between the baby’s and mother’s blood until the baby is born.
However, if she has a second baby who is also Rh positive, then it is possible that Rh antibodies from the mother’s blood will move across the placenta and enter the unborn baby’s bloodstream. These antibodies will then bind with the baby’s Rh positive red blood cells, causing them to be destroyed.
As a result of this, the baby may be born seriously ill, and unless a blood transfusion is given shortly after birth, the baby could die.
In each subsequent pregnancy the mother becomes more sensitised to Rh positive blood and produces antibodies earlier and earlier in each one. In severe cases, the baby may die before birth if a large amount of blood cells are destroyed.
This lack of compatibility between a mother's blood and that of her baby may sound worrying but, fortunately, medical science has developed a method to ensure the problems resulting from incompatible blood are minimised.
Doctors give an injection of Rh antibodies, in the form of ‘anti-D’ immunoglobulin, to a mother who has Rh negative blood within a few hours after she has given birth to a baby with Rh positive blood. This destroys any Rh positive blood cells which have been transferred to her from the baby, preventing her from producing antibodies that might harm future babies. Like all vaccines, ‘anti D’ is not 100 per cent effective in all cases, however, it can help protect the health of future pregnancies for many women.
To prevent early sensitisation, doctors also give women with Rh negative blood an anti D injection at 28 weeks of pregnancy and again at 34 weeks, as well as after the birth of her baby.
Earlier or additional doses of anti D are also generally given if there is an episode of vaginal bleeding during the pregnancy, and when invasive tests such as amniocentesis or chorionic villus sampling are performed.
Women who have a miscarriage, an ectopic pregnancy or a termination of pregnancy will also need anti D, even if it is the first pregnancy, to protect future pregnancies.
Sometimes a woman’s Rh antibody levels need to be measured periodically during her pregnancy to anticipate whether the baby might have problems. If her antibody levels are too high, then she might need further tests to check the health of the unborn baby. Sometimes the unborn baby needs a blood transfusion, or it might need one soon after birth.
On your first visit to a doctor during your pregnancy, you will usually have your blood type checked so that the problems described above can be avoided or minimised.
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Rhesus negative blood and pregnancy
You may be told you have rhesus negative blood during pregnancy screening. Read about the impact your Rh factor can have and what this means for you and your baby.
At your first antenatal appointment you are likely to be offered several blood tests. One of the tests is to find out your blood group. Your blood may be in one of four groups: A, B, AB or O.
The blood will also be either ‘rhesus positive’ or ‘rhesus negative’. People whose blood is rhesus positive have a substance known as D antigen on the surface of their red blood cells. Rhesus negative people do not. About 15% of women are rhesus negative. This isn’t usually a concern for a first pregnancy, but it may mean some extra care is needed to avoid problems if you get pregnant again.
Does my baby have the same type of blood as I do?
A woman with rhesus negative blood in pregnancy can be pregnant with a rhesus positive baby if the baby’s father is rhesus positive. If any of the baby’s blood enters the woman’s bloodstream, the woman’s immune system can develop antibodies (infection-fighting proteins) against the rhesus antigens. This is known as sensitisation. A transfer of blood can occur during birth, or if the woman has a bleed or an injury.
Risks of rhesus negative blood in second pregnancy
Production of the antibodies is not a problem in a first pregnancy, but when a woman with a rhesus negative blood type is pregnant next time with a rhesus positive baby, her antibodies can attack that baby’s red blood cells. This can result in a serious condition called haemolytic disease of the newborn, which leads to anaemia and jaundice in the baby.
If the woman is given an injection of a solution called ‘Anti-D’, it will ‘mop up’ any rhesus positive antigens, preventing production of antibodies against the baby. Anti-D injections reduce the risk of a rhesus negative woman becoming sensitised.
NICE recommends routine antenatal administration of Anti-D to all rhesus negative women in case sensitisation occurs. This can be given as a one-off dose at 28-30 weeks or as two doses at 28 and 34 weeks. It is quite safe for both the mother and the baby.
NCT’s helpline offers practical and emotional support in all areas of pregnancy, birth and early parenthood: 0300 330 0700. We also offer antenatal courses which are a great way to find out more about birth, labour and life with a new baby.
NICE provides guidance for women and their partners on Routine antenatal anti-D prophylaxis for women who are rhesus D negative.
Rh Negative Blood and Pregnancy
As soon as your pregnancy is confirmed your midwife or doctor will recommend blood tests to determine your immunity to various illnesses, as well as your overall health, your blood type and your Rh factor. Not everybody knows what their blood type is as it generally doesnвЂ™t affect us in a day-to-day sense. However in pregnancy it becomes important, as does the knowledge of whether you are Rh positive or negative.
What do Rh negative and Rh positive mean?
Everyone has a blood type (O, A, B or AB) and also a positive or negative rhesus or Rh factor. If you are Rh negative (also referred to as Rh (D) negative), this means your red blood cells do not have the D antigen. The D antigen is a protein carried on the red blood cells of people who have Rh positive blood types. Seventeen percent of the population are Rh negative and this is also influenced by ethnicity.
What is the significance of Rh negative blood and pregnancy?
A foetus inherits its blood type from both its mother and its father, therefore your baby may not have your blood type. An Rh negative mother for instance may carry an Rh positive baby.
Normally this isnвЂ™t an issue unless the foetal blood enters the motherвЂ™s blood stream. If this occurs then the motherвЂ™s body will develop antibodies to destroy Rh positive antigens because it recognises these as foreign cells. This is quite similar to the way the human body develops antibodies to fight viruses and provide ongoing immunity when a person comes into contact with a transient illness.
If the motherвЂ™s body develops antibodies to Rh positive blood then this can have catastrophic effects on future pregnancies as the antibodies cross the placenta and attack the foetusвЂ™ positive red blood cells. This can cause severe anaemia, fluid retention, swelling and brain damage in the foetus, and potentially foetal heart failure and death. This condition is called Haemolytic Disease of the Newborn or HDN.
How can foetal blood cross into the motherвЂ™s blood stream?
Foetal blood can cross into the motherвЂ™s blood stream without the mother being aware of it. The most likely time this will happen is during childbirth thus affecting future pregnancies. Times when foetal blood may cross into the motherвЂ™s blood stream include:
- Childbirth (affecting future pregnancies)
- Miscarriage beyond 12 weeks gestation
- Ectopic pregnancy
- Termination of pregnancy
- Chorionic Villus Sampling (CVS)
- Vaginal bleeding during pregnancy
- External Cephalic Version (ECV)
- An accident resulting in a hard blow to the stomach
Who is at risk?
Only mothers who have Rh negative blood are affected in pregnancy. Mothers who are Rh positive are not affected even if their baby is an Rh negative blood type. If an Rh negative mother is carrying an Rh negative baby then this will not affect her or her baby in this pregnancy. However we do not commonly know our babyвЂ™s blood types before birth to determine if the baby is Rh positive or Rh negative.
How can Rh negative mothers protect their pregnancies?
If you have an Rh negative blood type your caregiver will recommend you receive two injections during pregnancy, at 28 weeks and 34 weeks respectively, and a third injection following childbirth. These injections are Rh (D) immunoglobulin, commonly referred to as the anti D injection, which means they prevent the motherвЂ™s body creating antibodies to fight the positive blood group of this foetus or future foetuses. It is important to note that if the mother already has the Rh antibodies, the immunoglobulin will be ineffective as it is a preventative only.
The anti D injection is made of blood plasma and has been used since the 1960вЂ™s with no major adverse reactions known to affect either the mother or the foetus. In rare cases it may cause a mild allergic reaction in the mother such as a rash or flu-like symptoms. Therefore it is advisable to remain at the hospital or doctors clinic for 20 minutes following the first injection.
What happens if I develop Rh positive antibodies?
The development of antibodies against Rh positive blood is called rhesus disease and occurs in 16% of Rh negative women if not given the anti D injection. This is referred to as sensitisation which means the antibodies easily cross the placenta into the babyвЂ™s amniotic fluid and blood stream via the umbilical cord in future pregnancies.
If rhesus disease is present then the level of sensitisation will determine the level of monitoring or interventions needed. If levels of antibodies are low then your baby may not require any treatment. In more serious cases s/he may require phototherapy, a treatment used for jaundiced newborns. Your baby may also require blood transfusions in utero or after birth to speed up the removal of bilirubin in his/her blood.
Bilirubin is produced during the normal breakdown of red blood cells. When bilirubin is present in quantities above what the liver can excrete, it causes an orange tinge to the skin and eyes known as jaundice, which we sometimes see in newborns.
Need more information?
The Australian Red Cross Blood Service (2010) has produced an informative, easy to understand brochure for pregnant women who are Rh negative which can be found here. Your midwife or doctor will also be able to provide you with information regarding Rh negative blood types and the anti-D injection.
Article written for Pregnancy Birth and Beyond on 14 th October 2014
Australian Red Cross Blood Service 2010, You and your baby: important information for Rh (D) negative women, CSL Biotherapies, Australia.
Dean, L. 2005, Blood groups and red cell antigens, National Center for Biotechnology Information, United States.
National Health Service 2013, Rhesus disease, United Kingdom.
NSW Health 2014, Maternity вЂ“ Rh (D) Immunoglobulin (Anti D), Sydney.