multifetal pregnancy

 

 

Multifetal Pregnancy

Ina S. Irabon, MD, FPOGS, FPSRM,
FPSGE
Obstetrics and Gynecology
Reproductive Endocrinology and Infertility
Laparoscopy and Hysteroscopy

Reference

¡ Cunningham, Leveno, Bloom, etal. Williams

Obstetrics, 24th ed. 2014. Chapter 45

Outline

1. MECHANISMS OF MULTIFETAL GESTATIONS

2. DIAGNOSIS OF MULTIPLE FETUSES

3. MATERNAL ADAPTATION TO MULTIFETAL PREGNANCY

4. PREGNANCY COMPLICATIONS

5. ABERRANT TWINNING MECHANISMS

A. Conjoined twins

B. External parasitic twins

C. Fetus in fetus

6. VASCULAR ANASTOMOSES

A. TTTS

B. TAPS

C. TRAP

D

Outline

8. FETAL DEMISE

7. DISCORDANT GROWTH OF TWIN FETUSES

9. PRENATAL CARE AND ANTEPARTUM MANAGEMENT

10. DELIVERY ROUTE

A. Diet

B. Fetal surveillance

C. Tests of Fetal Well Being

A. cephalic-cephalic

B. cephalic – noncephalic

C. Breech first twin

D. triplets or higher order multiple gestation

Mechanism of multifetal
gestation

¡ Dizygotic / Fraternal twins – result from

fertilization of two separate ova

¡ Monozygotic / Identical twins – arise from a

single fertilized ovum that divides

¡ Either or both processes may be involved in

the formation of higher numbers.

¡ Quadruplets may arise from as few as one to

as many as four ova.

The outcome of the monozygotic twinning
process depends on when division occurs…

¡ Diamnionic, dichorionic:

If zygotes divide within the first 72
hours after fertilization, 2
embryos, 2 amnions, and 2
chorions develop

¡ Diamnionic, monochorionic:
If division occurs between the
fourth and eighth day

¡ Monoamnionic, monochorionic:

approximately 8 days after
fertilization, when the chorion
and the amnion have already
differentiated, and division results
in two embryos within a
common amnionic sac,

2-cell stage

A

B

C

D

0–4 days

Multifetal Pregnancy

893

C

H

A

P

T

E

R

4

5

4–8 days

Amnionic
cavity

Shared
amnionon

8–12 days

Chorionici
cavity

or

Shared
chorionion
chor

> 13 days

Separate
placenta

Fused
placenta

Dichorionic
diamnionic

Monochorionic
diamnionic

Monochorionic
monoamnionic

Monochorionic
monoamnionic
conjoined twins

FIGURE 45-1 Mechanism of monozygotic twinning. Black boxing and blue arrows in columns A, B, and C indicate timing of division.
A. At 0 to 4 days postfertilization, an early conceptus may divide into two. Division at this early stage creates two chorions and two

amnions (dichorionic, diamnionic). Placentas may be separate or fused. B. Division between 4 and 8 days leads to formation of a

blastocyst with two separate embryoblasts (inner cell masses). Each embryoblast will form its own amnion within a shared chorion

(monochorionic, diamnionic). C. Between 8 and 12 days, the amnion and amnionic cavity form above the germinal disc. Embryonic

division leads to two embryos with a shared amnion and shared chorion (monochorionic, monoamnionic). D. Differing theories explain

conjoined twin development. One describes an incomplete splitting of one embryo into two. The other describes fusion of a portion of

one embryo from a monozygotic pair onto the other.

evaluated with sonography in the first trimester have shown

tation. It has been estimated that 1 in 80 births are multifetal,

s

that one twin is lost or “vanishes” before the second trimester

whereas 1 in 8 pregnancies begin multifetal followed by sponta

s

–

in up to 10 to 40 percent of all twin pregnancies (Brady, 2013).

neous reduction of one or more embryos or fetuses (Corsello,

The incidence is higher in the setting of ART.

2010).

Monochorionic twins have a significantly greater risk of

Dickey and associates (2002) described spontaneous reduction

abortion than dichorionic twins (Sperling, 2006). In some

in 709 women with a multifetal pregnancy. Before 12 weeks, one

cases, the entire pregnancy aborts. In many cases, however, only

or more embryos died in 36 percent of twin pregnancies, 53 per-

one fetus dies, and the remaining fetus delivers as a singleton.

cent of triplet pregnancies, and 65 percent of quadruplet preg-

Undoubtedly, some threatened abortions have resulted in death

nancies. Interestingly, pregnancy duration and birthweight were

and resorption of one embryo from an unrecognized twin ges-

inversely related to the initial gestational sac number regardless

Factors that influence
twinning

¡ Race

¡ Maternal age

¡ Parity

¡ Heredity

¡ Nutrition

¡ Infertility treatment

¡ Pituitary gonadotropins

Multifetal Pregnancy

897

C

H

A

P

T

E

R

4

5

Sonographic Determination of
Chorionicity

¡ Two separate placentas suggest

dizygosity.

¡ Dichorionic:

¡ thick dividing membrane (>2

mm).

¡ Twin peak sign/lambda sign:

triangular projection of placental
tissue between the layers of the
dividing membrane

¡ dividing membrane less than 2-

mm thick

¡ T-sign:

right-angle relationship
between the membranes and
placenta; No extension of
placenta between the dividing
membranes

¡ Monochorionic:

A

A

Amnion

Chororororrrorrrrioiioioioiooooioooooioooioonnnnnnnnnnnn

B

Amnion

Chorion

B

FIGURE 45-4 A. Sonographic image of the “twin-peak” sign,

also termed the “lambda sign,” in a 24-week gestation. At

the top of this sonogram, tissue from the anterior placenta is

seen extending downward between the amnion layers. This

sign confirms dichorionic twinning. B. Schematic diagram of

the “twin-peak” sign. A triangular portion of placenta is seen

insinuating between the amniochorion layers.

FIGURE 45-5 A. Sonographic image of the “T” sign in a mono-

chorionic diamnionic gestation at 30 weeks. B. Schematic dia-

gram of the “T” sign. Twins are separated only by a membrane

created by the juxtaposed amnion of each twin. A “T” is formed

at the point at which amnions meet the placenta.

■ Sonography

By careful sonographic examination, separate gestational

sacs can be identified early in twin pregnancy (Fig. 45-7).

Subsequently, each fetal head should be seen in two per-

pendicular planes so as not to mistake a cross section of the

fetal trunk for a second fetal head. Ideally, two fetal heads

or two abdomens should be seen in the same image plane,

to avoid scanning the same fetus twice and interpreting it as

twins. Sonographic examination should detect practically all

sets of twins. Given the increased frequency of sonographic

examinations during the first trimester, early detection of a

twin pregnancy is common. Indeed, one argument in favor of

routine first-trimester sonographic screening is earlier detec-

tion of multiple fetuses.

Higher-order multifetal gestations are more difficult to eval-

uate. Even in the first trimester, it can be difficult to identify

the actual number of fetuses and their position. This determi-

nation is especially important if pregnancy reduction or selec-

tive termination is considered (p. 919).

FIGURE 45-6 Dichorionic diamnionic twin placenta. The mem-

brane partition that separated twin fetuses is elevated and con-

sists of chorion (c) between two amnions (a).