Five week pregnancy ultrasound with sac and yolk sac
Transvaginal ultrasound, normal pregnancy at 5 weeks 2 days
Gestational sac (black area ) and yolk sac are seen
Sac measures 6.25mm diameter
Yolk sac (small white circle in left side of the sac)
Yolk sac is a source of nutrients for the fetus
The fetus is too small to be seen this early in pregnancy
Ultrasound of another pregnancy at same gestational age as above. This shows identical (monozygotic) twins – 1 gestational sac with 2 yolk sacs visible inside it. This results from an early embryo dividing into 2 genetically identical embryos
The vast majority of twins from assisted reproductive technology procedures are not “identical”, but result from implantation of 2 embryos that were the result of fertilization of 2 different eggs, as shown in the ultrasound below.
Fraternal twins result from implantation of 2 genetically different embryos. Yolk sacs and fetal poles (the early fetus) are seen in 2 completely separate sacs. This pregnancy is at 6 weeks
