Just a short note to discuss a common mistake done by the defaults of most ultrasound machines between 11 - 14 weeks. The default for DBP used by popular equipments can get wrong GAs equivalences up to 10 days from a realiable LMP and in disagrreemnt with CRL and femur.
In most centers we are confortable with measurements of CRL, DBP, HC and FL falling within a window of 6-7 days from a working LMP. For example, a DBP for 20 mm is 12 weeks according to Jeanty and others. The same measurement (20 mm) renders values that are around 13+4 weeks, making difficult to come up with a "operational LMP" and often changing it for an operational LMP whichs is goes back up to 10 days. In general, I think that reliable, regular, menses every 26-30 days are very hard to be modified. Blood expelled from the uterus as a result of hematic remains or the overrated implantation bleeding, are both quite recognizable clinically and frequently not in synchrony with previous menses, so you can stick with your question "When did you initiate your last spontaneous menstural period? Did it follow your non-farmacoligical regular pattern as usual?
Just silly details to avoid confusions.
WIth my best wishes for our society, please receive a enthusiastic hello from the most beautiful Maternity -in and out- of the very soth of the world.
Ricardo Gómez, Cedip
Villarrica y nodo lacustre, La Araucanía, Chile.