There is so much grace in the thankfulness you have expressed, and it is right to give thanks that the Lord has shown mercy in moving the placenta to where it should be. That is His kindness, and it is good to acknowledge His hand in it.
I understand the weight you carry as you pray for continued protection. After the heartbreak of a stillbirth, and with concerns about diabetes and fibroids and things you cannot see or control, fear can press very hard. Fear can take hold of a heart and become debilitating, and it often comes when our eyes are fixed on the threat. The Scripture speaks of a secret place of safety, which is simply making God Himself your dwelling place, living your conscious life in Him, in whom we live and move and have our being. When you abide there under the shadow of the Almighty, He becomes your fortress and strength, the One in whom you trust. His promise is that He delivers from the snare of the fowler, from the hidden traps, and because you have set your love upon Him and known His name, He will answer when you call and set you on high.
Remembering the Lord is the cure for fear. David said though I walk through the valley of death I will fear no evil for You are with me. Fear and faith cannot rule the heart at the same time. Where fear is allowed to take over, faith departs, but where there is strong confidence in God, fear must leave. This does not mean you ignore wise and prudent care with your doctors, but it means you do not let fear motivate you. You can remember that greater is He who is with you than any threat that is against you.
Take encouragement also to keep praying with persistence. Zacharias prayed for years for a son and the angel finally said your prayer is heard, and with God nothing shall be impossible. Mary simply said be it unto me according to Your word. In the same way, we have a great High Priest, Jesus the Son of God, who has passed into heaven for us. Because He is holy and undefiled and ever lives to represent us, we can come boldly to the throne of grace to find mercy and help in time of need.
So I join you in prayer now. Father, in the name of Jesus, I thank You for Your mercy already shown in this pregnancy. I ask You to keep Your protecting hand upon this mother and upon this child. Guard them from complications from diabetes, from fibroids, and from any unseen problem. Grant a healthy carrying of this child to full term and a safe delivery. Replace fear with settled faith and peace as this dear one dwells in Your presence and remembers that You are with her. Let Your will be done and let Your strength and mercy be clearly seen. Amen.