This information fact sheet is designed to give you information as given to patients attending the Hammersmith Hospital HHT Clinic in London, England. We cannot advise you on whether you should or should not become pregnant (your own doctors are best placed for individual advice), but we can let you know how pregnancy might be different if you have HHT, and how to manage it as safely as possible.

During pregnancy the circulating blood may increase by as much as 60%, which is normal and essential for the development of the baby. This means fragile blood vessels may be more prone to bleed. The body copes with this extra blood by making many of the mother’s blood vessels dilate, and these do not always return to their pre-pregnancy size. In spite of this, the majority of HHT pregnancies are safe for the mother with HHT and for the baby.

You are probably aware that HHT affects members of you family in different ways, even though everyone with HHT in any one particular family will have the same genetic defect. This suggests that factors other than the mutated gene contribute to how HHT develops in any one individual, and this includes pregnancy-related complications.

When we looked at a series of 161 HHT pregnancies, 11 women had significant complications. Importantly, all except one of these women had close female relatives who had successful, uncomplicated pregnancies. The women belonged to eight different HHT families, with different genetic mutations, and there appeared to be nothing special about these families. So just because a family member has or has not suffered a complication does not mean that the same will happen to you.

Two published reports have now shown that the miscarriage rate is comparable in HHT and non-HHT pregnancies. Obviously, on average, one-half of the babies born to an HHT mother (or father) will go on to develop HHT, but there is no evidence for additional abnormalities developing more commonly that in non-HHT pregnancies.

It is import to realise that even if pulmonary AVM’s (PAVM’s) have caused a very low blood oxygen level in the mother, the baby can still develop normally, though amongst the women in our series with the lowest oxygen levels, premature births of healthy but small babies were common. If you have low oxygen levels, your baby’s growth would probably be carefully watched by your obstetrician.

Most pregnancies result in no serious HHT-related complications for the mother. Nosebleeds usually get worse, and new telangiectases often develop, but some women actually report an improvement in nosebleeds, and new skin lesions often improve post pregnancy. There are four important considerations for you:

1. PAVM growth: In our series, in six pregnancies, PAVMs developed or enlarged during pregnancy. Since our initial description, we have witnessed consistent and near-predictable growth of PAVMs, though often there is some spontaneous improvement in the first six months or so post delivery. In most of our ladies who displayed PAVM growth, further embolizations are need, but there is not necessarily an overall deterioration over the years.

In women in whom pregnancy precipitates the growth of previously undetectable PAVMs, it is not know if these would have gone on to develop later in life, in the absence of pregnancy. Overall, women with HHT are more prone to PAVMs than men (on average, of 100 individuals with PAVMs due to HHT, 62 will be women and only 38 will be men). However, the excess of PAVMs in women could also reflect the effects of female hormones in the absence of pregnancy, as seen in other aspects of HHT: In some women, nosebleeds vary through the menstrual cycle and menopause, and Dr. Eric Cutsem has clearly demonstrated benefits of oestrogen-progesterone therapy in heavily transfusion-dependant patients. Avoiding pregnancy does not mean you will avoid PAVMs.

2. PAVM bleed in pregnancy: In our series, two out of 161 pregnancies were complicated by life threatening last trimester bleeding from untreated PAVMs in the mother. This risk has been highlighted in another report from the Yale group. Although this is a very low risk for any one individual, it is why we recommend treatment of any PAVMs before pregnancy. Embolization in the second and third trimesters is also possible, as demonstrated by a recent paper demonstrating the safety of embolization performed in two North American centres between 16 and 36 weeks gestation. You and your doctors should be aware that in late pregnancy you cough up any blood which cannot be accounted for by a nosebleed, this should be considered a medical emergency.
3. Cerebral AVM (CAVM) bleeds: There is no good data that CAVMs in HHT or non-HHT patients are more likely to bleed during delivery or even pregnancy. However, the risk of cerebral AVM bleeds remain an understandable concern, particularly as there are instances when bleeds have coincided with pregnancy. In our series, three of the 161 pregnancies were complicated by strokes, though with full recoveries made by two of the tree patients. Since 10% of HHT patients will have problems during their pregnancy, you will realise that many women with CAVMs will have normal pregnancies.
4. Spinal AVMs: Most anaesthetists would use the 1-2% risk of spinal AVMs that is quoted for HHT to say that an epidural is too risky, and you will probably be offered alternative analgesia. However, if referred early, MRI scans could be carried out to exclude AVMs and allow epidural analgesia.

1. The first message is "Don’t Panic" Women with HHT have been having children for centuries. If you know you have PAVMs or CAVMs it is important for you to discuss the possibility of pregnancy with specialist doctors.
2. Before pregnancy, it is important to check if you have PAVMs. How you are screened will vary according to where you are, as different methods are effective. PAVMs tend to run in families, but there is always the first case in a family, so we recommend PAVM screening for everyone with HHT. Your doctors will try to treat any PAVMs before you become pregnant. You will probably also be advised to use prophylactic antibiotics before dentistry or surgery (including delivery).
3. When you are planning to become pregnant, don’t forget to follow all the usual prenatal advice about alcohol, cigarettes, folic acid, and checking that any regular dietary items or medications would be safe in early pregnancy.
4. During pregnancy, if there is any bleeding from the lungs (coughing up blood), you need urgent review by doctors who can diagnose and treat PAVMs. Embolization is possible even in the later stages of pregnancy. If doctors are checking your oxygen levels, they need to remember that although levels usually drop when PAVMs are present, during pregnancy, other factors may make oxygen levels rise from pre-pregnancy values, even if PAVMs are enlarging.
5. Prior to delivery, your obstetrician needs to know that there is a small risk of spinal AVMs.
6. The mode of delivery will be decided by your obstetrician, guided by your general health and particular features of your pregnancy. If PAVMs are present you will need prophylactic antibiotics. If cerebral AVMs are present you may be offered a caesarean section to avoid excessive straining.
7. Following pregnancy, PAVM screening may need to be repeated, even if initially normal.
8. Try to enjoy your pregnancy, and let your doctors do the thinking for you.

Adapted from an article originally published in HHT Foundation International Direct Connection Winter 1997, and updated August 2002.

This Pamphlet was prepared by Dr Claire Sholvlin, Senior Lecturer and Honorary Consultant Physician, Hammersmith Hospital and Imperial College, London. In conjunction with Dr James Jackson, Consultant Interventional Radiologist, Hammersmith Hospital, Professor Michael de Swiet, Consultant Obstetric Physician, Queen Charlotte’s and Chelsea Hospital and Dr Wendy Taylor, Consultant Interventional Neuroradiologist, London.

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