There have been case reports suggesting that IVF children may also be more prone to developing cancer. A letter to the Lancet (22 December, 1990) spoke of five children born between 1985 and 1987 in Australia who developed brain tumours. The researchers believed that the common factor among them was the use of Clomid (clomiphene) to stimulate ovulation. Another study from La Trobe University in Australia looked at all live births (5249) following IVF at two clinics in Victoria, and checked these with a cancer registry. What they found was a slight increase in cancer incidence over that expected (Hum Reprod, 2000; 15: 604-7).

Early reports of assisted conceptions found that 7 per cent of the infants were born with major congenital malformations - ranging from heart abnormalities to clubfoot (Lancet, 1991; 337: 762-3). This compares with a 2-per-cent rate in the general population. Heart malformations were the greatest problem, accounting for almost 4 per cent of cases, compared with the usual rate of around 0.4-0.5 per cent.

IVF babies have also been linked to a cluster of rare genitourinary birth defects called cloacal-bladder exstrophy-epispadias complex. The Johns Hopkins Children’s Center has evaluated 12-14 per cent of all such cases in the US. Of 78 children treated at the Center during 1998-2001, four were IVF births. The expected incidence for all IVF children born during the study period (112,137) was five, indicating that the defects could be seven times more widespread in IVF children than in the general population (J Urol, 2003; 169: 1512-5).

Another problem coming to the surface are rare genetic imprinting defects. Imprinting ‘marks’ certain genes - notably, those associated with the development of the baby in the womb - to distinguish whether they have come from the mother’s egg or the father’s sperm. This reveals how active a gene is. Fathers’ genes tend to make babies grow faster while those from mothers tend to slow growth down. Disruption of imprinting means a loss of control.

One example of such a disruption is the Beckwith-Wiedemann syndrome (BWS), a collection of defects characterised by excessive growth of various tissues. Its incidence is about 1 in 15,000 births overall. US scientists studying the national registry of BWS patients found six times more IVF-initiated conceptions registered than expected (Am J Hum Genet, 2003; 72: 156-60).

Imprinting problems may also arise through a procedure called ICSI (intracytoplasmic sperm injection), which involves injecting a single sperm directly into the egg. In two cases of Angelman’s syndrome (also known as happy puppet syndrome, a condition akin to autism), the researchers concluded that ICSI may interfere with the maternal imprint in the pre-embryo cell (Am J Hum Genet, 2002; 71: 162-4).

ICSI is also suspected of causing mild genetic abnormalities, including passing the father’s infertility to the child as, ordinarily, only the strongest sperm succeeds in getting through to the egg. ICSI may also play a role in brain defects. One study found that, at age one, 17 per cent of ISCI children showed mild-to-significant delayed development compared with 2 per cent of those conceived by ordinary IVF and 1 per cent of those conceived naturally (Lancet, 1998; 351: 1524-5).

Lord Winston himself is especially concerned about the safety of using frozen embryos and the procedure of blastocyst transfer, where embryos are not placed back into the body for up to five days, instead of the usual two, after fertilisation. This delay may be the cause of potential genetic abnormalities (Nat Cell Biol, 2002; 4 [Suppl 1]: S14-8; Nat Med, 2002; 8 [Suppl 1]: S14-8).