Pregnancy, Parturition & Lactation & IVF

Question 1

Rupture of membranes, without active labor in a 32-year-old patient on her 40th week of gestation leads you to start induction of labor and delivery with an intravenous drip of pitocin (oxycotin analog). Which of the following best summarizes the uterine changes (increases or decreases) that have occurred during pregnancy that will contribute to enhanced responsiveness to pitocin?

Answer 1

Prostaglandin synthesis ↑, Gap-function formation ↑, Oxycotin-receptor expression ↑

The uterus, fetal membranes and placenta produce prostaglandins (PGs). PGs initiate contractions, which are augmented & sustained by oxytocin. Increases in both gap junctions and oxytocin receptors enhance myometrial contractility.

Question 2

A 30-year-old female patient arrives at your office because of missed menstrual periods for 2 months. Her history indicates regular menstrual periods in the past. During physical examination, you suspect that she may be pregnant. Which laboratory values would be compatible with your diagnosis?

Answer 2

High urinary hCG and high plasma progesterone

Estrogens and progesterone gradually increase and remain elevated through pregnancy. hCG peaks in the 1st trimester, then declines and reaches a plateau. See notes pg 5 & pg 1150.

Question 3

A 34-year old-woman begins assisted fertility treatment to initiate ovulation. She is treated with an agent that acts via gonadotropin-releasing hormone (GnRH) receptors in the anterior pituitary. Which of the following treatment is most likely to be effective?

Answer 3

GnRH agonist given in pulsatile doses

Pulsatile GnRH mimics the physiologic release pattern. Continuous dosing is ineffective because it downregulates pituitary gonadotropes.

Question 4

A couple trying to conceive decided to use an ovulation predictor kit to indicate when intercourse should occur to maximize the probability of pregnancy. If ovulation occurs on day 15 of this woman’s menstrual cycle, when would implantation of a successfully fertilized egg most likely occur in the uterus?

Answer 4

Days 21 - 22

Implantation normally occurs 6 - 7 days after ovulation.

Question 5

An experiment was performed in vitro in which motile sperm were placed in a dish with an egg that was released by natural ovulation. The sperm and egg were both loaded with fluorescent dyes that allowed intracellular [Ca2+] to be measured. A calcium signal was recorded in a single sperm, attached to the zona pellucida of the egg. This signal was most likely associated with which of the following events?

Answer 5

ACROSOMAL EXN

Binding of the sperm head to specific proteins of the zona pellucida causes a calcium signal in the sperm, resulting in the acrosome reaction. Also see notes pg 2 & pg. 1147.

Question 6

Which of the following enzymes or substrates does the fetus provide for the placenta to produce estrogen?

Answer 6

Dehydroepiandrosterone sulfate (DHEA-S)

Human placenta has a very high aromatase enzyme activity that converts androgens to estrogens but lacks the ability to produce the androgen substrate. DHEA-S and its 16-hydroxylated derivative are produced by fetal adrenal for this purpose. Also see notes pgs 9-10 & 1154-1155.

Question 7

A 23-year-old woman consulted her midwife 1 day after the uncomplicated delivery of her first child. She was concerned about her lack of milk production and that she was only producing “a thin yellow fluid” at the breast. The midwife reassured her that this was normal and that milk production would begin within 1-2 days. Which hormone was suppressing her milk production?

Answer 7

ESTROGEN

Estrogens suppress the milk-producing effects of prolactin during pregnancy to prevent milk production before birth. Expulsion of the placenta at birth removes the source of estrogen. At about day 2 postpartum, milk production in response to prolactin begins. Also see notes pgs 16-17 & 1161-1162.

Question 8

A 37-year old-woman who is breast-feeding her 4-month-old son is taking the train to see her mother who lives several hours away. When the woman hears the cry of another infant, she notices that milk has been expressed from both her breasts. The release of which hormone can account for this response

Answer 8

OXYTOCIN

The lactation reflex occurs in response to a baby suckling, which produces a surge of oxytocin secretion and milk ejection. This reflex can be conditioned by stimuli such as the sound of a baby crying

Question 9

32-year-old woman and her partner were trying to conceive a child. The woman had regular menstrual cycles of about 30 days in length. Four days after missing her menstrual period, she bought a commercial pregnancy testing kit. The couple was excited to discover that her urine sample indicated a positive result for pregnancy. Which of the following hormones was detected in her urine?

Answer 9

Human chorionic gonadotropin

Human chorionic gonadotropin is a pregnancy-specific hormone secreted by the early embryonic trophoblast. Trace amounts can be detected in urine as early as 7-10 days after ovulation.

Question 10

A young woman is given daily injections of a substance beginning on the 16th day of her normal menstrual cycle and continuing for 3 weeks. As long as the injections continue, she does not menstruate. The injected substance could be which of the following?

Answer 10

HCG

HCG has the same stimulatory effect as LH on the corpus luteum. Administration of HCG would cause the corpus luteum to continue to secrete estrogen and progesterone, preventing degradation of the endometrium and onset of menstruation.

Question 11

Which of the following could inhibit the initiation of labor?

Answer 11

Administration of an antagonist of prostaglandin E2 effects

Antagonism of progesterone’s effects, dilation of the cervix, and oxytocin all increase uterine smooth muscle excitability and will facilitate contractions and onset of labor. LH would have no effect. PGE2 strongly stimulates uterine smooth muscle contraction and is formed in increasing rate by the placenta late in gestation.

Question 12

RU486 causes abortion if it is administered before or soon after implantation. What is the specific effect of RU486?
Answer
Selected Answer:

Answer 12

It blocks progesterone receptors so that progesterone has no effect within the body

Progesterone is required to maintain the decidual cells of the endometrium. If progesterone levels fall, as they do during the last days of a nonpregnant menstrual cycle, menstruation will follow within a few days, with loss of pregnancy. Administration of a compound that blocks the progesterone receptor during the first few days after conception will terminate the pregnancy.

Question 13

During pregnancy, the uterine smooth muscle is quiescent. During the 9th month of gestation the uterine muscle becomes progressively more excitable. What factors contribute to the increase in excitability?

Answer 13

Progesterone synthesis by the placenta decreases

Very high plasma concentration of progesterone maintains the uterine muscle in a quiescent state during pregnancy. In the final month of gestation the concentration of progesterone begins to decline, increasing the excitability of the muscle.

Question 14

The placenta does which of the following?

Answer 14

Secretes estrogen

The placenta secretes both estrogen and progesterone from the trophoblast cells.

Question 15

Where does fertilization normally take place?

Answer 15

Ampulla of the fallopian tubes

Question 16

Why is osteoporosis much more common in elderly women than in elderly men?

Answer 16

Men continue to produce testosterone throughout their lifetime, whereas women cease estrogen production after menopause

Testosterone stimulates the cellular functions of bone that lead to bone formation. Testosterone secretion from the interstitial cells declines with age, but it continues at sufficient levels to stimulate bone formation throughout a man’s lifetime. Conversely, estrogen production in women falls after menopause, leaving the bones without the stimulatory effect of estrogen. As a result, osteoporosis is common in women after menopause.

Question 17

A 30-year-old woman is breast-feeding her infant. During suckling, which of the following hormonal responses is expected?

Answer 17

Increased secretion of oxytocin from the paraventricular nuclei

During suckling, stimulation of receptors on the nipples increases neural input to both the supraoptic and paraventricular nuclei. Activation of these nuclei leads to the release of oxytocin and neurophysin from secretion granules in the posterior pituitary gland. Suckling does not stimulate the secretion of appreciable amounts of ADH.

Question 18

CHALLENGE QUESTION: During the latter stages of pregnancy, many women experience an increase in body hair growth in a masculine pattern. What is the explanation for this?

Answer 18

The maternal and fetal adrenal glands secrete large amounts of androgenic steroids that are used by the placenta to form estrogen

Estrogen secreted by the placenta is not synthesized from basic substrates in the placenta. Instead, it is formed almost entirely from androgenic steroid compounds that are formed in both the mother’s and the fetus’s adrenal glands. These androgenic compounds are transported by the blood to the placenta and converted by the trophoblast cells to estrogen compounds. Their concentration in the maternal blood may also stimulate hair growth on the body