Forced labour? Birth is more a hostile takeover

At the start of his book, David Bainbridge describes pregnancy as a uniquely intimate association between two people. Just how intimate is revealed to us chapter by chapter in a riveting tale of escalating possessiveness. Not only does a foetus dismantle its mother's immune system, which is designed specifically to repel invaders and visitors, it colonises her body like a rampant parasite. While still a free-floating embryo and using genes left behind by ancestral virus infections, it spews out proteins that force the uterine tissues to fuse with it.

It is the first step in the embryo's hostile takeover of the innocent mother and a sign of the uncompromising savagery to come. This ball of cells literally chews its way into the uterine wall with the aggressiveness of a caterpillar on its favourite leaf. Like a malignant cancer, the baby's cells crawl through the walls of the mother's blood vessels into direct contact with her blood. And then, in an act of chutzpah unrivalled in the animal kingdom, they line the mother's own blood spaces, luxuriating in pools of life-supporting maternal blood.

Embracing this embryonic slayer is the mother's first of many acts of unconditional love. A mother's biological selflessness is all the more astonishing as it demands the redesigning of the uterine wall to cope with the onslaught of the burrowing baby. Evolution has had to teach the uterus to fortify itself into a thick buffer zone to absorb the ferocity of the baby's attack. It is this baby-buffer zone that has to be shed each month at menstruation if a woman does not become pregnant.

Now we can see the grand design behind human pregnancy: the menstrual cycle with its glandular accessories, wave upon wave of hormones, follicle ripening and rupture, endometrial sloughing - all are simply the scaffolding that jacks up the act of conception.

A woman's body has evolved the way it has solely to form the perfect resting place for a ball of vandalising cells that needs to bury itself deep inside the wall of the womb to stay put and survive. In the selfishness stakes, a foetus leaves a gene standing.

This insight explodes off the page, as do many others throughout this book. It reads like a whodunit (the culprit is always the foetus). A ripping yarn and irresistible - I read it at one sitting. One is left wondering how pregnancy proceeds at all, teetering as it does on the brink of incredibility at every turn. Give me the breathtaking ingenuity of sperm penetration over the origin of black holes every time.

Pregnancy is natural and may be a miracle. Bainbridge's account of pregnancy, however, demands the defiance of nature and the acceptance of miracles at molecular level, let alone at the levels of genes and hormones. Producing a baby is a negotiation of minefields. It is Darwinism up close and personal. The survival of the fittest -Jthe survival of your baby at the expense of your body.

Through Bainbridge's eyes, we see that the foetus calls the shots from the moment of fertilisation. You thought you were having a baby. This book shows that your baby is having you. Having you on, in fact, fooling you with the cleverest nine-month-long biological sleight of hand imaginable. Given a window of opportunity lasting only a week, the pinhead embryo fools a woman's body into not having another period, which would spell the end of it. In seven days, a woman's body has somehow to recognise that she is pregnant. The embryo has to convince her, and she has to acquiesce. And yes, we know that the embryo succeeds, but only by hijacking her brain.

Technicalities in this book are leavened by zinging metaphors and a racy prose style, making it pretty much an effortless read. I am particularly grateful to Bainbridge for supplying the science to support the use of the morning-after pill in the face of the pro-life lobby, which claims that it aborts an independent being. I always knew the morning-after pill was not an abortifacient: conception, possibly even fertilisation, has not had time to happen by the morning after.

No, what I learned from this book is pertinent to the concept of independent life. The early embryo, possibly until it is two weeks old, is not independent. It relies on its mother's genes. It is able to discriminate between its own and its mother's genes, and it preferentially chooses to use the latter. Thus, at the time the morning-after pill is swallowed, the embryo is still, genetically at any rate, part of its mother.

Miriam Stoppard, FRCP, is a doctor and writer.