A sperm nucleus and an oocyte nucleus have just fused in the uterine tube. What single-cell stage exists immediately afterward?

The one-cell product of fertilization begins mitotic cleavage as it moves toward the uterus. What stage comes next?

An early embryo has divided several times but remains a solid ball of cells with no internal cavity. Which stage is it?

A solid ball of embryonic cells reaches the uterus and then develops a fluid-filled cavity. Which stage forms next?

A hollow early embryo has an inner cell mass and an outer layer that will help form the chorion. What happens next in normal development?

An early embryo has embedded in the uterine lining and begins receiving support from maternal tissue. Which stage has just occurred?

After the blastocyst embeds, the inner cell mass will form the embryo. Which developmental period begins after the first two weeks?

Which structure is built from fetal chorionic tissue and maternal uterine tissue to exchange gases, nutrients and wastes?

Which membrane forms a fluid-filled sac that cushions the developing embryo and helps maintain a stable watery environment?

Which outer extraembryonic membrane helps form the fetal side of the placenta?

Which tube carries fetal blood to and from the exchange organ through two arteries and one vein?

Which vessels carry oxygen-poor fetal blood from the fetus toward the placenta?

Which vessel returns oxygen-rich blood from the placenta to the fetus?

Which extraembryonic structure first helps nourish the early embryo before the placenta is fully functional?

By the end of which trimester are the major organ systems laid down, making harmful exposures most likely to cause structural defects?

During which trimester does rapid body growth make fetal movement easier for the mother to feel?

A fetus is gaining most of its final weight, and the lungs are maturing for breathing after birth. Which trimester is this?

The heart begins beating and limb buds appear during early organ formation. Which trimester includes these events?

External genitalia become easier to identify and the skeleton becomes more ossified on ultrasound. Which trimester is most associated with this?

Fat builds up under the fetus's skin, and the fetus usually turns head-down in the uterus to get ready for birth. Which trimester is this?

A urine test detects a hormone that appears soon after implantation and keeps the corpus luteum active. Which hormone is it?

Which hormone keeps the uterine lining thick and reduces uterine muscle contractions during pregnancy?

Which hormone rises near delivery and stimulates strong rhythmic contractions of the uterine muscle?

Which hormone prepares mammary glands for milk production after birth?

Which ovarian and placental hormone increases blood flow to the uterus and helps the reproductive tract enlarge during pregnancy?

During pregnancy, a hormone makes the mother's cells less responsive to insulin so more glucose remains available to the fetus. Which hormone is it?

Regular contractions are thinning the cervix and opening it from 0 cm toward 10 cm. Which stage of labor is occurring?

The cervix is fully open and the fetus moves through the birth canal. Which stage of labor has begun?

After the baby is delivered, contractions continue until the afterbirth is pushed out of the uterus. Which stage of labor is this?

In labor, pressure on the cervix triggers oxytocin release, which makes contractions stronger. What feedback pattern is this?