Fetal anemia in monochorionic twins: a review on diagnosis, management, and outcome

Figures & data

Table 1. Prevalence and type of fetal anemia for different types of MC twin complications.

	TAPS	Chronic TTTS	Acute peripartum TTTS	Perimortem exsanguination
Prevalence of fetal anemia	~100%	2–15%	~100%	~50%
Type of anemia	Chronic	Chronic^a	Acute	Acute
Cause	Chronic transfusion through minuscule anastomoses	Chronic transfusion through large anastomoses	Acute transfusion through large bidirectional anastomoses	Acute transfusion from the living twin to the demised co-twin
Treatment	Best antenatal treatment is unclear	Fetoscopic laser surgery	No antenatal treatment, this condition occurs during labor	Expectant, or rescue IUT
Severe cerebral injury	4–11%	5–10%	unknown	26–32%
Perinatal mortality	9–18%	~25%	8%	16% (in co-twins)

^aCompared to acute peripartum TTTS and perimortem exsanguination, anemia in TTTS donors is more chronic in nature. However, anemia in chronic TTTS may develop quicker than in TAPS, as anastomoses in chronic TTTS are larger. TAPS, twin anemia polycythemia sequence; TTTS, twin-twin transfusion syndrome.

Figure 1. (a) Sonographic image of placental dichotomy, with hyperechogenic hydropic placental share for the TAPS donor and flattened hypoechogenic placental share for the TAPS recipient. (b) Cardiomegaly in the TAPS donor. (c) Starry-sky liver in the TAPS recipient.

Table 2. Antenatal classification system for TAPS.

TAPS stage	Findings at Doppler ultrasound examination
Stage 1	A delta MCA-PSV > 0.5 MoM Without other signs of fetal compromise^a
Stage 2	A delta MCA-PSV > 0.7 MoM Without other signs of fetal compromise^a
Stage 3	As stage 1 or 2, with cardiac compromise of the donor, defined critically abnormal flow
Stage 4	Hydrops in the donor
Stage 5	Intrauterine demise of one or both fetuses preceded by TAPS

TAPS, twin anemia polycythemia sequence; MCA-PSV, middle cerebral artery – peak systolic velocity; MoM, multiples of the median.

^afetal compromise is defined as critically abnormal flow: Doppler shows absent or reversed end-diastolic flow in umbilical artery, pulsatile flow in umbilical vein and/or increased pulsatility index or reversed flow in ductus venosus.

Figure 2. A MC twin pair with spontaneous twin anemia polycythemia sequence illustrating the characteristic large skin color difference.

Figure 3. An overview of placental differences between TAPS (upper row) and acute peripartum TTTS (lower row). Placentas have been injected with colored dye. Blue (arteries) and red (veins) were used for the first-born twin and green (arteries) and yellow (veins) were used for the second-born twin. (a) Fetal side of the a placenta from spontaneous TAPS. The left placental share belongs to the recipient twin, the right placental share belongs to the donor twin. (b) Color dye injection revealed only one minuscule veno-arterial anastomosis (red-green). (c) The maternal side of the TAPS placenta shows a striking color difference with a plethoric share for the recipient and a pale share for the donor. (d) Fetal side of a placenta from a acute peripartum TTTS twin. The left placental share belongs to the recipient twin, the left placental share to the donor twin. (e) Color dye injection revealed numerous large anastomoses including an arterio-arterial anastomosis (blue-green). (f) The maternal side of the acute peripartum TTTS placenta shows no color difference.