You can read the whole study at PLOS. The conclusion:
A simple, individualised, Mediterranean-style diet in pregnancy did not reduce the overall risk of adverse maternal and offspring complications but has the potential to reduce gestational weight gain [but not by much] and the risk of gestational diabetes [by 35%].
Source: Mediterranean-style diet in pregnant women with metabolic risk factors (ESTEEM): A pragmatic multicentre randomised trial
PS: Don’t try to lose weight during pregnancy without professional help.