According to Zenit.org the Vatican has approved and made available to dioceses in the United States the Rite for the Blessing of a Child in the Womb. Considered to be an Effective Witness to the Sanctity of Human Life, the text of the blessing which is in both English and Spanish, can be found online at the USCCB website www.usccb.org/about/pro-life-activities/prayers/pro-life-blessings.cfm
Also according to Zenit.org the request for the blessing originated with our own Archbishop Joseph Kurtz when he was then-Bishop of Knoxville, Tennessee.
Here is an Excerpt taken from Rite of Blessing for a Child in the Womb
give constant protection and grant a healthy birth that is the sign of our rebirth one day into the eternal rejoicing of
(For the Mother)
Lord, who have brought to this woman the wondrous joy of motherhood, grant her comfort in all anxiety
and make her determined to lead her child along the ways of salvation.
(For the Father)
Lord of the ages, who have singled out this man to know the grace and pride of fatherhood, grant him courage in this new responsibility, and make him an example of justice and truth for this child.
(For the Family)
Lord, endow this family with sincere and enduring love as they prepare to welcome this child into their midst.
(For the Community)
Lord, you have put into the hearts of all men and women of good will a great awe and wonder at the gift of new life; fill this (parish)community with faithfulness to the teachings of the Gospel and new resolve to share in the spiritual formation of this child in Christ our Savior, who lives and reigns for ever and ever.