Nipple stimulation can help release the hormone oxytocin, which may encourage labor to start. It’s a natural method that some people find effective. However, it should be done under the guidance of your healthcare provider to ensure it’s safe for your pregnancy. 

There are situations where nipple stimulation might not be appropriate. If you have a high-risk pregnancy, are at risk of preterm labor, or have certain complications like placenta previa or a history of uterine surgery, nipple stimulation could potentially lead to excessive contractions or distress for the baby. These strong contractions could decrease the baby's oxygen supply, leading to complications.

Your healthcare provider can give you specific instructions and let you know if this method is appropriate for your situation. They can also monitor you for any adverse reactions to ensure both your safety and the baby’s well-being. It’s important to approach this technique carefully to avoid any potential complications and to use it only under professional supervision.