The impact of prenatal diagnosis on the incidence of haemophilia in Sweden

Management of carriers and babies with haemophilia

Although up to 30% of babies born with haemophilia do not have a family history of the disorder, the remaining 70% are born in families where haemophilia has been diagnosed. It has been estimated that for each male with haemophilia, there are five potential female carriers. Such women will benefit from knowledge of both their genetic (mutation present or not) and phenotype (level of plasma factor activity) status. Genetic counselling services to provide information and testing, together with plasma factor measurement, should be offered where available to all women at risk of being carriers. It is critical that women know their plasma factor measurement as they may have mild haemophilia (factor 5-30%, reference range 50-150%) which requires management at times of medical and surgical procedures and following trauma. Close liaison between adult and paediatric haemophilia centres and obstetric-gynaecology units is important to ensure that clinical carers identify and address carriers' needs. Genetic testing should be performed only after a potential carrier has been counselled and supported to receive such information. There is no coercion to accept such testing. An advantage of genetic testing is to then discuss pre-implantation genetic diagnosis which is an ex-vitro form of prenatal diagnosis. This can assist couples at risk of having a child with haemophilia who wish to reduce their anxieties about reproduction. Approximately 4% of boys with haemophilia, born in countries with good maternal care, will have intracranial haemorrhage in the neonatal period. There are no high-level evidence-based guidelines for the management of delivery or of the newborn with haemophilia. Obstetricians or other birth attendants need to be advised of the possibility of delivery of a boy with haemophilia and seek support from a haemophilia specialist during the pregnancy. The mother can then be monitored and plans for delivery be developed between her medical consultants and discussed with her. It is always preferable for a carrier to know of her genetic and phenotypic status before becoming pregnant so that she is informed as to her options and requirements for safe delivery.

A global view on prophylaxis: possibilities and consequences

Prophylactic infusion therapy, both primary and secondary, has proven of great benefit to patients with haemophilia, specifically those with severe disease or bleeding episodes and patterns that have lead to development of arthropathy. At this time, optimal outcome in patients with severe haemophilia has been proven achievable with primary prophylaxis initiated at an early age in a regimen of three times weekly or every other day for patients with factor VIII deficiency, and twice weekly for those with factor IX deficiency. Despite the demonstrated benefit of primary prophylaxis, this treatment regimen has not been uniformly adopted into clinical practice even in developed countries. In developing countries, where issues of allocation of precious health care resources are of paramount importance, access to adequate treatment for persons with haemophilia on a programme of on-demand therapy is not commonly available; the cost of primary prophylaxis, even with intermediate purity plasma-derived factor concentrates or plasma fractions such as cryoprecipitate, renders this treatment the exception rather than the rule.

Reproductive choices of haemophilia carriers

The actual reproductive choices made by slightly over a quarter of all the carriers of severe or moderate haemophilia in Sweden were investigated and compared with those of a randomly selected age-matched group of women who were not carriers of haemophilia. In general, the 105 carriers had the same number of children as other women of similar age. However, carriers who did not choose prenatal diagnosis (PD) often abstained from further pregnancies after the birth of a haemophilic child, and they had significantly fewer children than the remainder of the carriers, as well as fewer children than women in the control group. Logistic regression analysis showed choice of PD to be correlated to a positive attitude towards abortion following PD and a family history of haemophilia. Carriers who have experienced the complications of haemophilia or its treatment appear to be more in favour of PD than women whose haemophilic children have received modern treatment without complications.

Prenatal diagnosis of haemophilia

Genotype assessment based on direct identification of the pathogenic mutation in a chorionic villi sample obtained in the 11-12th gestational week is the most reliable method for prenatal diagnosis and should be used if available. Genetic linkage studies of polymorphisms should be the second choice in the assessment of carriers and in prenatal diagnosis. Carriers of haemophilia should be offered adequate psychosocial support before, during and after the prenatal diagnostic procedures.

Carrier testing and prenatal diagnosis of haemophilia--utilisation and psychological consequences

Attitudes towards prenatal diagnosis, and abortion vary widely between different countries, religions, cultures and over time. Carrier testing and prenatal diagnosis (PD) of haemophilia have become an integrated part of the comprehensive care for haemophilia in Sweden as well as in many other countries. Almost all carriers are interested in carrier testing if they are aware of the possibility. With the development of PD by chorionic villus sampling in the first trimester, the method became acceptable for many carriers, and it has in Sweden actually had an effect on the incidence of haemophilia in the 1990s. The use of PD is more common among women who perceive haemophilia as a very serious disease and who have a positive attitude towards legal abortion. The main reason for carriers not to use PD was that they do not find haemophilia to be a sufficiently serious disorder to justify an abortion. Women and their spouses are under a great deal of psychological pressure in association with the PD procedure, and the psychological consequences of having to terminate a pregnancy are long-lasting. At follow-up, about 6 years after PD and abortion, these women, however, do not have more signs of psychological distress than women without PD experience. Nevertheless, they must be offered qualified assistance both before and after PD as well as adequate follow-up after an abortion to help them cope with the emotional strain they are under.

Prenatal diagnosis of haemophilia

Prenatal diagnosis of haemophilia A or B is possible by means of chorionic villus biopsy in the first trimester which traces the mutation or informative genetic markers. If possible, direct gene analysis of the mutation is preferred. The natural starting point in haemophilia A is to ascertain whether the disease is due to inversion in the X-chromosome, which is the case in almost half of the severe cases. In haemophilia B, most families carry a unique mutation which needs to be characterized. In the immediate future, much of the prenatal diagnosis will be based on indirect genetic markers, repeats or polymorphisms, of the F.VIII and IX genes. Today chorionic villus sampling is the most widely used method but amniotic fluid, fetal blood and pre-implantation genetic diagnostics can also be used in selected cases. Prenatal diagnosis must be preceded by adequate genetic counselling and risk assessment of the potential carrier and subsequent support during the diagnostic process.