Ultrasounds and dating conception
The chance of selection of more than one dominant follicle in the same cycle increases with maternal age as evidenced by a higher incidence of fraternal twins in older women.In addition, with hormonal treatment for induction of ovulation and other assisted reproduction procedures, multiple follicles can grow to preovulatory size capable of ovulation in one cycle.
The explanation for how this can happen lies in the evidence that more than one crop (or wave) of follicles is available from which to select a follicle for ovulation, contrary to the traditional understanding of the process.
In very early pregnancy, the embryo and pregnancy sac may simply be too small to see very much at all.
But with every day which passes, the embryo becomes bigger and more advanced in its development.
When having a transabdominal ultrasound, however, a full bladder is necessary in order to “lift” the uterus up and out of the pelvis so the embryo can be seen more clearly.
Later on as the pregnancy progresses, a full bladder is not necessary as the enlarging uterus is no longer contained in the pelvic rim.