Blueprint Exam 1 OB
WEEK 1:
Twins: Dizygotic vs. Monozygotic
● Dizygotic (double ovulation):
o Fraternal (nonidentical) twins
o (double ovulation – 2 eggs - meaning they arise from separate ova fertilized by 2 separate
spermatozoa.
o 2 chorions; 2 amnions
o There are two umbilical cords, two chorions, and two amnions; sometimes the placentas sometimes
fuse and look as if they are one.
o Can be the same or different sexes.
o Dizygotic twinning increases with maternal age to about 35 then decreases abruptly. Dizygotic
twins tend to occur in certain families, because of genetic factors that result in elevated serum
gonadotropin levels, leading to double ovulation. Among all groups, as parity increases, so does the
chance for multiple births.
● Monozygotic twins – Identical:
○ 1 egg divides after fertilization into 2 separate zygotes; form from a single fertilized ovum.
○ They are of the same sex and have the same phenotype (appearance). They also usually have a
common placenta.
○ They are also at greater risk for other complications like as congenital anomalies including
conjoining and twin to twin transfusion syndrome (TTTS)
○ TTTS is when blood moves from one twin to the other leaving one with too little and the other with
too much blood
○ Not affected by environment, race, physical characteristics or fertility.
○ The number of amnions and chorions present depends on the timing of the division.
● Twin to twin transfusion syndrome:
○ In a monochorionic placenta, there may be a vascular anastomosis that leads to twin-to-twin
transfusion syndrome. Blood is drained from one fetus to the other in. The donor fetus becomes
growth restricted, and oligohydramnios develops. The recipient fetus becomes polycythemic and
hydropic, and hydramnios develops. If the fetuses become severely affected during the second
trimester, untreated mortality may be 100%
Fetal Circulation
● Oxygenated blood flow: 1 vein
● Deoxygenated blood flow: 2 arteries
● Function of placenta:
o Placenta: breathes for the baby
o Lungs: Do not function because of the high pressure system and blood could go into the lungs.
● Blood leaves the placenta and enters the fetus through the umbilical vein. After circulating through the fetus,
the blood returns to the placenta through the umbilical arteries. The ductus venosus, the foramen ovale, and
the ductus arteriosus allow the blood to bypass the fetal liver and lungs.
,
Implantation - AKA nidation:
● Trophoblast(another name for zygote): After layer where it attaches to the upper 3rd. Must attach to the
endometrium for further nurishment. We want to implant it to the ampulla so there is vascular force.
● Where does implantation occur?
o Best site for implantation is the upper ⅓ of the uterus; the upper part of the posterior uterine
wall.
● Blastocyst: implants 7-9 days after fertilization, then sinks down into uterine lining until completely covered
o It is a fetus after week 12. The lining of the uterus thickens below the blastocyst and cells of
trophoblast grow down into the thickened lining, forming processes called chorionic villi.
● Decidua capsularis, basalis, vera:
o Decidua capsularis covers the blastocyst.
o Decidua basalis, Maternal portion, directly implanted beneath blastocyte. Forms the maternal part
of the placenta – contains a large number of blood vessels.
▪ Dirty Duncan
o Decidua vera(parietalis): lines the rest of the uterine cavity. Chorionic villi in contact with decidua
basalis will form the fetal portion of the placenta.
● Progesterone is high during plantation b/c it prepares the endometrium for pregnancy. The endometrium
increases in thickness and vascularity in preparation for implantation, the endometrium is called the decidua.
Placenta
● Formation of the placenta occurs during the 3rd week. The placenta does not produce hormones until
later 11th week.
● Composed of maternal portion and fetal portion:
o Maternal portion: decidua basalis and its circulation (dirty duncan).
o Fetal portion: Chorionic villi (Shiny Schultz) - covered by adherent amnion.
● Functions
o Exchanges nutrient and (Excretion)waste products between the embryonic and maternal
circulations.
o Fetal respiration
o Produces human placenta lactogen, estrogen and progesterone - it takes over the job of producing
all the hormones at week 11.
o 3rd trimester: transfer of immunoglobulins → providing the fetus with passive immunity
o Large particles (bacteria) cannot pass but smallers ones (VIRUSES - HIV, herpes simplex virus)
can.
● 5 hormones
o 3 are protein:
▪ HCG (human chorionic gonadotropin): Hormone tested for dipstick pregnancy test.
Blueprint Exam 1 OB
WEEK 1:
Twins: Dizygotic vs. Monozygotic
● Dizygotic (double ovulation):
o Fraternal (nonidentical) twins
o (double ovulation – 2 eggs - meaning they arise from separate ova fertilized by 2 separate
spermatozoa.
o 2 chorions; 2 amnions
o There are two umbilical cords, two chorions, and two amnions; sometimes the placentas sometimes
fuse and look as if they are one.
o Can be the same or different sexes.
o Dizygotic twinning increases with maternal age to about 35 then decreases abruptly. Dizygotic
twins tend to occur in certain families, because of genetic factors that result in elevated serum
gonadotropin levels, leading to double ovulation. Among all groups, as parity increases, so does the
chance for multiple births.
● Monozygotic twins – Identical:
○ 1 egg divides after fertilization into 2 separate zygotes; form from a single fertilized ovum.
○ They are of the same sex and have the same phenotype (appearance). They also usually have a
common placenta.
○ They are also at greater risk for other complications like as congenital anomalies including
conjoining and twin to twin transfusion syndrome (TTTS)
○ TTTS is when blood moves from one twin to the other leaving one with too little and the other with
too much blood
○ Not affected by environment, race, physical characteristics or fertility.
○ The number of amnions and chorions present depends on the timing of the division.
● Twin to twin transfusion syndrome:
○ In a monochorionic placenta, there may be a vascular anastomosis that leads to twin-to-twin
transfusion syndrome. Blood is drained from one fetus to the other in. The donor fetus becomes
growth restricted, and oligohydramnios develops. The recipient fetus becomes polycythemic and
hydropic, and hydramnios develops. If the fetuses become severely affected during the second
trimester, untreated mortality may be 100%
Fetal Circulation
● Oxygenated blood flow: 1 vein
● Deoxygenated blood flow: 2 arteries
● Function of placenta:
o Placenta: breathes for the baby
o Lungs: Do not function because of the high pressure system and blood could go into the lungs.
● Blood leaves the placenta and enters the fetus through the umbilical vein. After circulating through the fetus,
the blood returns to the placenta through the umbilical arteries. The ductus venosus, the foramen ovale, and
the ductus arteriosus allow the blood to bypass the fetal liver and lungs.
,
Implantation - AKA nidation:
● Trophoblast(another name for zygote): After layer where it attaches to the upper 3rd. Must attach to the
endometrium for further nurishment. We want to implant it to the ampulla so there is vascular force.
● Where does implantation occur?
o Best site for implantation is the upper ⅓ of the uterus; the upper part of the posterior uterine
wall.
● Blastocyst: implants 7-9 days after fertilization, then sinks down into uterine lining until completely covered
o It is a fetus after week 12. The lining of the uterus thickens below the blastocyst and cells of
trophoblast grow down into the thickened lining, forming processes called chorionic villi.
● Decidua capsularis, basalis, vera:
o Decidua capsularis covers the blastocyst.
o Decidua basalis, Maternal portion, directly implanted beneath blastocyte. Forms the maternal part
of the placenta – contains a large number of blood vessels.
▪ Dirty Duncan
o Decidua vera(parietalis): lines the rest of the uterine cavity. Chorionic villi in contact with decidua
basalis will form the fetal portion of the placenta.
● Progesterone is high during plantation b/c it prepares the endometrium for pregnancy. The endometrium
increases in thickness and vascularity in preparation for implantation, the endometrium is called the decidua.
Placenta
● Formation of the placenta occurs during the 3rd week. The placenta does not produce hormones until
later 11th week.
● Composed of maternal portion and fetal portion:
o Maternal portion: decidua basalis and its circulation (dirty duncan).
o Fetal portion: Chorionic villi (Shiny Schultz) - covered by adherent amnion.
● Functions
o Exchanges nutrient and (Excretion)waste products between the embryonic and maternal
circulations.
o Fetal respiration
o Produces human placenta lactogen, estrogen and progesterone - it takes over the job of producing
all the hormones at week 11.
o 3rd trimester: transfer of immunoglobulins → providing the fetus with passive immunity
o Large particles (bacteria) cannot pass but smallers ones (VIRUSES - HIV, herpes simplex virus)
can.
● 5 hormones
o 3 are protein:
▪ HCG (human chorionic gonadotropin): Hormone tested for dipstick pregnancy test.
