Lecture 53 Late Fetal Development and Twins

Question 1

What is the difference between embryonic age and gestational age?

Answer 1

gestational age is measured from LNMP, which overestimates by about 2 weeks (40 weeks gestational, 38 weeks embryonic on average)

Question 2

Fertilization to week 8 describes what critical period?

Answer 2

embryonic period

Question 3

What occurs during the embryonic period?

Answer 3

formation of primordia of all major organ systems

Question 4

What is the fetal period?

Answer 4

describes week 9 to birth and features rapid growth and differentiation of tissues/organ systems

Question 5

What is Nagele’s rule?

Answer 5

estimates expected date of delivery which = (LNMP - 3 months) + 1 year and 7 days

Question 6

What measurements are considered when performing second or third trimester dating?

Answer 6

biparietal diameter
head circumference
weight

Question 7

What measurement is taken as part of first trimester dating from 7-13 weeks?

Answer 7

Crown-Rump Length (CRL)

Question 8

What general factors can affect fetal growth?

Answer 8

maternal DM, poor nutrition, multiple gestations, smoking, drugs/alcohol, impaired uteroplacental blood flow, genetic disorders

Question 9

What times define the three trimesters and how long are each approximately?

Answer 9

First (weeks 1-13)
Second (weeks 14-27)
Third (weeks 28-40)
each are three months

Question 10

What is the function of the vernix caseosa that covers the fetus during the second trimester?

Answer 10

maintains fetal skin so that it does not break down in the watery environment
insulates once baby is born

Question 11

During which trimester does the mother feel movement, or “the quickening”?

Answer 11

second trimester

Question 12

During which trimester are all major organ systems formed?

Answer 12

first trimester

Question 13

During which trimester can most anomalies be seen on ultrasound and features mainly fetal growth and differentiation?

Answer 13

second trimester

Question 14

Why is fetal viability possible at the end of the second trimester?

Answer 14

surfactant is produced in the lungs by type II pneumocytes, allowing for baby to breath air

Question 15

What is chorion?

Answer 15

another name for the placenta

Question 16

The ____ sac is inside the _____ sac.

Answer 16

Amniotic; chorionic

Question 17

Twins that originate from two zygotes are called what?

Answer 17

dizygotic twins (2/3 of all twins)

Question 18

Dizygotic twins always have ____ amnions and ____ chorions, but they may fuse (40%).

Answer 18

2

2

Question 19

Maternal age, familial genetics, and ART all increase the liklihood of what event?

Answer 19

multiple gestation

Question 20

What event increases the risk for fetal growth restriction, twin-twin transfusion syndrome, congenital anomalies, and miscarriage/ premature births?

Answer 20

having monozygotic twins

Question 21

what are monozygotic twins?

Answer 21

twins that originate from one zygote (1/3 of twins)

Question 22

What determines chorionicity and amnionicity of twins?

Answer 22

type of placenta and membranes depend on when the twinning process occured

Question 23

For monozygotic twins, what timing of split results in dichorionic/diamniotic twins?

Answer 23

days 3-5

Question 24

For monozygotic twins, what timing of split results in monochorionic/diamniotic twins?

Answer 24

Days 5-8

Question 25

For monozygotic twins, what timing of split results in monochorionic/monoamniotic twins?

Answer 25

Days 8-13

Question 26

For monozygotic twins, what timing of split results in conjoined twins?

Answer 26

Day 13+

Question 27

Preterm is less than ____ weeks. Full term is ____ to ___ weeks. Post term is _____ weeks and beyond.

Answer 27

37
37 to 41
42

Question 28

Name some risk factors for preterm birth.

Answer 28

multiple gestations, prior preterm birth, uterine anomaly, excess anmiotic fluid, cigarettes/drug use, intrauterine infection