With most congenital malformations a baby is not large enough, or misshapen enough, to cause difficulty during labour. The important exceptions are anencephaly and hydrocephaly, for which you should use the methods below. If you have the misfortune to find a double monster, Caesarean section is the method of choice.
Anencephaly is complicated in 90% of cases by polyhydramnios (M 15.4); so when you diagnose this, X-ray a mother to see if her baby has a head. If he has not, he is usually stillborn, and even when he is born alive, he does not survive more than a few hours. When you have explained the diagnosis to her, she will usually insist that her pregnancy is induced.
Hydrocephaly is not always easy to diagnose clinically, and is often missed during pregnancy. A common mistake is to misdiagnose a brow presentation (when the head feels big) for hydrocephaly. If you suspect it, confirm the diagnosis by X-ray. If the diagnosis is then obvious, proceed as described below. If it is doubtful, wait. Even during labour the diagnosis is easily missed, if widely distended sutures and fontanelles cannot be felt.
THE HOPELESSLY MALFORMED FETUS ANENCEPHALY. [f41]If this is accompanied by polyhydramnios, drain the mother's amniotic sac slowly by draining her hindwaters with a Drew[nd]Smythe catheter. Alternatively, rupture her forewaters by making a small hole with an amnion hook. Give her an escalating oxytocin drip (19.3), and she will probably deliver promptly.
If anencephaly is not accompanied by polyhydramnios (10% of cases), pregnancy may be prolonged up to a year or more (rare), and make delivery difficult. Try PGE2 pessaries first (the ideal indication for them). Then try surgical induction and an escalating oxytocin drip (19.3). These will probably succeed. If you cannot induce her (19.3), you will have to do a Caesarean section[md]this is tragic, so avoid it if you can.
HYDROCEPHALY. [f41]If you make the diagnosis during pregnancy, induce labour, and try to avoid Caesarean section.
If you diagnose hydrocephaly when labour with a cephalic presentation has been in progress for some time, and the baby's head is more than minimally enlarged, you will have to make it smaller before you can deliver him. If he is dead, drain his CSF with a lumbar puncture needle. Some obstetricians would do this even if he is alive (draining his CSF does not kill him), others would wait for his heart to stop. If you are not sure of the diagnosis, or don't feel you can risk sacrificing him, you may be forced to section her.
To perforate his head, wait until dilatation has passed 3 cm, then drain his cerebrospinal fluid with a large needle between his widely separated skull bones, or, less satisfactorily, with Simpson's perforator. His collapsed head will slowly settle into his mother's pelvis, and he will deliver.
CAUTION ! If possible, perforate him before she is 5 cm dilated, because her over-distended lower segment may rupture if you don't.
If you diagnose hydrocephaly during a breech presentation, he will probably deliver spontaneously as far as his umbilicus (19.8). Progress will then be arrested as his hydrocephalic head fails to enter her pelvic brim. Draining his CSF will be less messy than a craniotomy: (1) If, at this stage you see the commonly-associated meningomyelocele, pass a steel or gum elastic male catheter through the spinal defect into his ventricles, to drain off his CSF. If he has no spina bifida, you can easily do a laminectomy with a scalpel, to allow the catheter to enter. Or, (2) pass a needle through his occipital bone into his skull. Or, (3) make sure that her bladder is empty, and then tap his aftercoming head abdominally with a large spinal needle.