At the time of ovulation (release of an egg from an ovary), conception takes place. This is usually 2
weeks after your last period. At the time of conception you are already 2 weeks pregnant, but this
would not show positive on a pregnancy test until approximately at least another 2 weeks. The
fertilised egg will be slowly moving along the fallopian tube to the womb and the cells will be
dividing again and again. Once in the womb it will implant and is now called an embryo. The first
you may know that you are pregnant is when your period does not arrive or you may have some
other symptoms such as breast tenderness, tiredness and or nausea.
In the early stages of pregnancy, the embryo is attached to a yolk sac. The yolk sac provides
nourishment to the developing embryo and is the first formation within the pregnancy sac (gestation
sac). It provides endocrine, metabolic and immunological functions and contributes to the
development of fetal gastrointestinal and reproductive systems. A yolk sac is seen in an
intrauterine pregnancy; and from 5.5 weeks , appears as a circular structure within the pregnancy
sac ( Gestation sac). If a tiny embryo at 5.5-6/40 is visible, it often looks like a little diamond on a
ring on an ultrasound scan.
A few weeks later, the placenta is formed and takes over in providing nourishment to the baby.
The yolk sac gradually disappears from 12-14/40 and is often no longer visible on ultrasound scan.

Debbie Hamilton-Rose
Nurse practitioner
Somerset Early Scans

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