A common misconception which most women have is that having conceived a child easily for the first time, means automatically that further pregnancies and children are secured. Unfortunately, this is clearly not the case. Having bared one child does give certain advantages, though.
You know that your uterus is hospitable and capable of growing a baby, that your body has wisdom of giving birth, and you have a generally more relaxed attitude about getting pregnant (or are simply too busy carrying about older children and can’t get as desperate as women who are stacked in the waiting process over a long time).
Still, aging is something that you can’t stop. Your eggs will age (meaning lose the capacity to give babies) in any case: if you are taking oral contraceptives, being repeatedly pregnant, suppressing ovulations due to years of lactating – aging continues inside just like on the visible surface of the body.
Even assuming that your partner’s sperm has high fertile potential which remains constant over time, and further assuming your own reproductive hardware stays fit (no endometriosis, ovulation issues, infections, or extreme changes of Body-Mass-Index), your ovaries will age and this is something you can’t entirely prevent. You can only slow it down an stretch your reproductive time to an extent. Some women can slow their biological clock for years, some much less, and this is something determined by our genetic and lifestyle.
That’s why understanding principles how to keep ovaries fresh and fit is essential for every women, regardless whether you previously had children or not.
To find out when you ovulate:
(I love simple LH-strips but some women prefer digital measuring):
Useful books about fertility and improving egg quality: