I am not entirely sure what you are asking but pregnancy does not start at a a specific age. In order to become pregnant a male must ejaculate (release seminal fluids containing sperm) inside the female's vagina once the female has reached her reproductive stages (usually around 11-14) and the sperm must fertilize the egg. A female is capable of becoming pregnant once she starts her menstrual cycle as a young woman.
The age of mating starts around age of 10-15 years old. The pregnancy length is usually 11 months. A female blue whale can only have 1 newborn at each time.
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The third trimester starts at week 28, or 7 months into the pregnancy.
No there is no heard and fast rule where your age and pregnancy are concerned.
Yes, 3 weeks into pregnancy is when implantation usually starts
15
the vocal chords
Peaceful till the sickness starts!
Most starts to show in the second trimester.
Teen age mothers.
33 is a perfectly suitable age for pregnancy. Birth defect rates don't start to rise until around the age of 40-45.
Usually, a pregnancy will start to show after the first 3 months!