This topic has been the reason most marriages crash and also why most relationships crash for different reasons. While in marriage the pregnancy is the utmost desire but in relationships, they usually don’t want pregnancy except they are married.
Read all here and let us hear your opinion: Why Do Married Women Face Difficulties In Conceiving But Single Ladies Get Pregnant Easily - http:///s26eb5934200122en_ng

Let me just give you some of the common reasons :

Note that this is my personal opinion on the issue.

1. Age: Due to the high standard of getting married. Most ladies hardly find husbands in the early age of 20s, which is highly fertile period for women. And at that tender age, most boys and girls may likely be infection free.
2. Stress and anxiety: As you may already know, worrying about a problem, makes it worst. It is different from thinking of a solution to it. Most women, from the very first day of marriage, they become to anxious for pregnancy plus the stress of their new wifely role. Whereas a girlfriend may not even be think of it at all.
3. Their husbands: Some may be married to men with fertility challenges. Whereas, if a boyfriend has sperm issues you will not even notice.
4. It could also be due to the pregnancy prevention drugs they take while dating and not leaving out wrong methods of abortion.
5. You only take not of the challenge when a woman is married. It equally affect people while dating. Just the society does not take note.

Funny enough, married women are getting pregnant everyday. Just that the few that are having the challenge tend to look like a lot because of how the society has put it.
Some people whose body need a little time to adjust to that of their partners before they could get pregnant are also added to the number. That is why you see a couple who has been married for just 3-6 months already complaining.

I can't click that link. But some things I know about this topic is that most married ladies find it difficult to conceive because of their previous lifestyle probably too many abortions, contraceptive pills, smoking habit etc, or it maybe heredity or family issue (family witchcraft, either from the man's family or the lady) or age (late marriage)

Peace

The most annoying part is how pregnant women(married) keep frustrating their husbands at the slightest chance. Vomit everywhere, pour saliva everywhere, select food and many frustrating stuffs. But you see the unmarried ones eh, nothing of such nature o, no complaints, nothing nothing na to just born fiaaaa.