Ritgen maneuver is done in :

Ritgen maneuver is done for delivery of head in normal labour to allow controlled delivery of head When the head distends the vulva and perineum enough to open the vaginal introitus to a diameter of 5 cm or more, a towel draped gloved hand maybe used to exe forward pressure on the chin of the fetus through the perineum just in front of coccyx. Concurrently the other hand exes pressure superiorly against the occiput. It also ours neck extension so that the head is delivered with its smallest diameters passing through the introitus and over the perineum. Ref: Datta Obs 9e pg 130.