Video Transcript
Why is a pregnant woman unlikely to have periods? (A) The cervix becomes blocked by the embryo, so no blood can leave the uterus. (B) Progesterone levels remain high to maintain the uterine lining, so ovulation is inhibited. (C) The uterus no longer produces a thick lining, so there is nothing to be broken down. Or (D) this is incorrect; a pregnant woman will still have periods.
The first thing we should know is that during a period, which is also known as menstruation, the uterine lining is broken down and shed through the vagina along with blood and any unfertilized egg cells. Fertilization occurs when a sperm cell fuses with an egg cell, which is also called an ovum. When an egg cell is fertilized, it forms a zygote, which will develop into an embryo. The embryo can then implant in the wall of the uterus.
Meanwhile, the Graafian follicle in the ovary that once contained the egg cell before it was released transforms into a structure called the corpus luteum. The corpus luteum releases progesterone to maintain a thick uterine lining, preparing it for the potential implantation of an embryo. In addition to maintaining this thick uterine lining, progesterone inhibits the release of the hormones FSH and LH from a gland in the brain called the pituitary gland. The presence of LH would normally stimulate ovulation, which is when the ovary releases an egg cell from one of the follicles into a fallopian tube. Therefore, if LH is not released, ovulation will not occur.
We mentioned earlier that a period is the result of the uterine lining breaking down. As the level of progesterone remains high to keep the uterine lining thick, there will be no ovulation and therefore no menstruation, or period. This means that the reason why a pregnant woman is unlikely to have periods, and the correct answer to this question, is (B). Progesterone levels remain high to maintain the uterine lining, so ovulation is inhibited.
