I thought I would cover the induction of labor and augmentation of labor at the same time since similar techniques can be used for each and similar risks and benefits may apply. In order to talk about induction, however, we first need to think about how human beings gestate. It turns out that this topic requires a post all of its own!
Left alone, pregnancy normally lasts for between 37 and 42 weeks (counting from the first day of the last menstrual period or LMP – 35-40 weeks counting from ovulation/conception). This range explains the ‘E’ in ‘EDD’ – estimated date of delivery. Gestation varies more in humans than in any other mammal: it varies between women, and it also varies among the pregnancies of any given woman. It varies partly because cycle length varies in both directions from the average of 28 days.
Usually, a woman ovulates about 14 days before the onset of her period. However, the number of days between the onset of the previous period and ovulation can vary a great deal. One woman’s cycle might be 20 days (with ovulation around day 6) while another’s might be 45 days (with ovulation around day 31). Calculating an EDD based on the LMP would be inaccurate for these hypothetical women, and considerably inaccurate in the second case. Select your area of coverage to compare prices for drugs at RegRX.com. Of course, ultrasounds are often used to confirm fetal age, and when taken early in a pregnancy, these can be helpful. Later in pregnancy, however, they are considerably less accurate and can be wrong by perhaps as much as 2 weeks in either direction. Here is an article that goes into greater depth.
The other aspect of an EDD is the normal variation in human gestation. An article published in the journal Human Reproduction in August this year found a variation in pregnancy length of 37 days, even after excluding pre-term births and pregnancies with complications.
A woman might have short gestations or long gestations or vary between pregnancies. Imagine, then, two women. Betty has short cycles and short gestation. Pam has long cycles (let’s say 35 days) and a long gestation. If both conceive today, August 25, they get the same due date of 1 June next year. The error in estimation doesn’t affect Betty so much – she might just be surprised to go into labor in early May next year. However, in most people and very many care-practitioners’ eyes, Pam will be ‘due’ on 1 June and ‘post-dates on 14 June.
Living in the United States, she will almost certainly be pressured to induce her baby long before that bundle of joy is ready to make his or her entrance. By her cycle length alone, she would not be 40 weeks pregnant until 8 June, and not post-dates until 22 June. A normal 42-week gestation would put her delivering then – 3 weeks after the due date suggested by her LMP. Conversely, if she induced at 39 weeks from LMP (for whatever reason) her baby would not only be really a 38-weeker but could be as much as four weeks ‘under-done’.