ICL 18.1: Embryology and the Menstrual Cycle

Question 1

what phase is oocyte in after ovulation occurs?

Answer 1

prophase of meiosis II

before that, it’s in metaphase of meiosis I

after that, once it’s fertilized it will complete meiosis II

Question 2

what is fertilization?

Answer 2

post conception day 0

Question 3

what day are we when there is a blastocyst?

Answer 3

day 5

day 6 is when the blastocyst actually implants; it’s the beginning of implantation and then it’s totally buried into the endometrium by day 10

in general, post conception day 0 till day 10 is when the zygote implants in the uterus

Question 4

what does a pregnancy test test for?

Answer 4

hCG

at implantation, the blastocyst attaches on day 6 to the endometrium and then the trophoblasts differentiate into 2 types of trophoblasts, the syncytiotrophoblasts and cytotrophoblasts

the syncytiotrophoblasts are what make hCG and they don’t form until after implantation and differentiation, usually around day 9!!

so even though at day 6 you’re definitely pregnant but it’s not till day 10 that there is enough hCG being produced to be detected on the test since the syncytiotrophoblasts aren’t totally differentiated

Question 5

why is hCG important?

Answer 5

hCG is essential for the function of the corpus luteum which produces progesterone and estrogen early on in the pregnancy until the placenta takes over

it has also been linked to early pregnancy symptoms like nausea and vomiting

it’s eliminated in the urine and can be detected by pregnancy tests around day 9 after fertilization

Question 6

how do we date a pregnancy?

Answer 6

you need to know the start of the last menstrual period!

ask if they have regular cycles too and ask how many days they usually are

ask if they were using OCPs because they can be inhibiting ovulation even though the patient may be having a period!

Question 7

what is gestational age?

Answer 7

the number of weeks that have elapsed since the first day of the last menstrual period

usually this is the conceptional age + 2 weeks

Question 8

what is conceptional age?

Answer 8

the number of weeks that have elapsed since fertilization

Question 9

how can you predict the due date?

Answer 9

1. you can subtract 3 months and add one week from the first day of the LMP
2. add 267 days from the date of ovulation

Question 10

what are the pregnancy milestones?

Answer 10

1. early US
2. 10-12 weeks: fetal heart tones first audible
3. 16-20 weeks: fetal movement
4. 20 weeks: uterine fundus at umbilicus