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WEEK 5 OF GESTATION |
- Embryonic pole can be distinguished at 5 weeks and 3-4 days.
- Embryo ± 2mm. Growth = 1mm/day.
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Normal video
at 5 weeks of gestation - CRL = 4mm
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- Heart.
- Cardiac activity begins at 5 weeks 2 days, but may not be appreciated until embryo = 5mm in size, but should always be seen when embryo > 5mm (6 weeks 4 days).
- Cardiac activity can usually be detected endovaginally on day 27-29 or as soon as the embryonic pole is visualized (1).
- The heart rate is only 70-90 beats / minute (2).
- Primitive and two chambered, with blood flow from the venous to the arterial side in a sequential manner.
- Ventricular chamber enlargement occurs at about 40 days from LMP.
- Gestational sac can be identified as early as 4 weeks 3 days and can be routinely detected endovaginally after 5 weeks.
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- Double Bleb.
- Double sac structure, which represents the developing yolk sac and extraembryonic coelom.
- Present for only 2-3 days.
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4+5 weeks ·
Gestational sac ·
Yolk sac not visible |
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5+1 weeks ·
Gestational sac ·
Yolk sac visualized. |
- Configuration of the Embryo.
- The embryo is initially visualized as an echogenic area of thickening on the yolk sac.
- Straight until it reaches 3-4mm in length (on ultrasound the embryo is a straight echogenic line adjacent to the yolk sac and close to the vitelline duct). Occasionally it cannot be seen, but the prominent pulsations of the embryonic heart reveal its presence.
- Flexion into a C-shape as the embryo grows. (greatest length of embryonic pole = neck rump length as head is flexed).
- CRL can be measured at ± 9 weeks GA when fetus = 18-22mm.
REFERENCES |
- Schats R, Jansen AM, Wladimiroff JW. Embryonic heart activity: appearance and development in early human pregnancy. Br J Obstet Gynaecol 1990;97:984-994.
- Levi CS, Lyons EA, Zheng XH et.al. Endovaginal ultrasound: demonstration of cardiac
activity in embryos less than 5mm in crown-rump length. Radiology 1990;176:71-74.