How a Mother’s Body Adjusts to Pregnancy
The changes in the mother’s own body during pregnancy are enormous. The womb itself grows from the sixe of a small orange to the size of a large fat squash to become by far the biggest muscle in the human body, male or female. This is not only done by stretching. New muscle fibers develop, and the old ones grow thicker and longer.
To supply the womb and the growing baby inside, the mother’s blood supply increases by as much as a third. This accounts for the pregnant woman’s great need for iron, which is required to make the new red blood cells. The blood pressure often drops, especially in the middle third of pregnancy, as blood vessels relax under the influence of placental hormones. The extra blood increases the work load of the heart and, although its rate and rhythm of beating should not change during pregnancy, its size must, by anything up to forty percent. And it has to enlarge while being by the growing womb as the pregnancy progresses.
This is one reason why a woman will cope with pregnancy better if she is physically fit before it starts. It is also the main reason why she should not put on too much weight during pregnancy; the more weight, the more work for the heart.
The mother’s lungs too are pushed up into her chest, which gradually expands, the ribs spreading to make room. The mother may find herself talking shorter and lighter breaths, punctuated at intervals by deep sighs, because placental hormones affect the brain center controlling the depth and speed of breathing.
The demands on the heart and lungs explain why in the last two months. The squeezing of all her other organs can cause some discomfort too, although very rarely actual pain. There is no doubt that whatever the joys of parenthood the last six weeks of pregnancy can be a wearisome time of waiting. Even simple things like peeling potatoes or getting a toddler off to nursery school are an unexpected effort.