I am a Christian and want to know what verse should I read to encourage me about infertility.
The inability to have children has long been a problem for couples. The first mention of barrenness was with Sarah, Abraham's wife (Genesis 11:30). In their case, it was a situation God left unchanged until they had lived well beyond the normal age for having children in order to prove a point. "And not being weak in faith, he did not consider his own body, already dead (since he was about a hundred years old), and the deadness of Sarah's womb. He did not waver at the promise of God through unbelief, but was strengthened in faith, giving glory to God, and being fully convinced that what He had promised He was also able to perform" (Romans 11:19-21). This is not to say that God will always grant children if a person has enough faith. In the case of Abraham and Sarah, God had told them they would have a child when they had long stopped expecting one and their acceptance of God's promise was evidence of their faith that God would carry out what He had offered.
It is proper to ask God for children. "Now Isaac pleaded with the LORD for his wife, because she was barren; and the LORD granted his plea, and Rebekah his wife conceived" (Genesis 25:21). How God determines to answer such prayers is, of course, up to Him. Hannah's prayer for a child is also an illustration of this (I Samuel 1).
Lest we forget, it isn't always the woman who is unable to have children. "Now Absalom in his lifetime had taken and set up a pillar for himself, which is in the King's Valley. For he said, "I have no son to keep my name in remembrance." He called the pillar after his own name. And to this day it is called Absalom's Monument" (II Samuel 18:18).
For so many children come so easily, even when they are not expected or wanted, that many people forget that, in reality, children are a blessing from God. "Behold, children are a heritage from the LORD, the fruit of the womb is a reward" (Psalm 127:3). Those who desire children and cannot easily have them are often more appreciative of the blessing.
Still, what God tells us is that the key to happiness isn't in having children. God offers much more:
"Do not let the son of the foreigner who has joined himself to the LORD speak, saying, "The LORD has utterly separated me from His people"; nor let the eunuch say, "Here I am, a dry tree." For thus says the LORD: "To the eunuchs who keep My Sabbaths, and choose what pleases Me, and hold fast My covenant, Even to them I will give in My house and within My walls a place and a name better than that of sons and daughters; I will give them an everlasting name that shall not be cut off. Also the sons of the foreigner who join themselves to the LORD, to serve Him, and to love the name of the LORD, to be His servants - everyone who keeps from defiling the Sabbath, and holds fast My covenant - even them I will bring to My holy mountain, and make them joyful in My house of prayer. Their burnt offerings and their sacrifices will be accepted on My altar; for My house shall be called a house of prayer for all nations"" (Isaiah 56:3-7).
What saddens me more is the insistence of couples that their children must come from their own bodies. It should not be forgotten that our relationship with God is described as one of adoption. "But when the fullness of the time had come, God sent forth His Son, born of a woman, born under the law, to redeem those who were under the law, that we might receive the adoption as sons. And because you are sons, God has sent forth the Spirit of His Son into your hearts, crying out, "Abba, Father!" Therefore you are no longer a slave but a son, and if a son, then an heir of God through Christ" (Galatians 4:4-7). It is a statement of the extra special love that a parent chooses to adopt a child and make him as if he was his own.