 The investigators will pick out two areas of most severe striae gravidarum on a participants abdomen. One of the areas will be treated by fractional laser once every three months for 2 times combined with PRP injection once a month for 6 times. Another area will be treated by nanofat grafting once every three months for 2 times and PRP therapy once a month for 6 times. The participants were asked to come back 1369 months after treatment for further follow-up. 