If the cycles are regular about 28 days apart, that would put the pregnancy at 7 weeks. This is a gestational age at which an intrauterine pregnancy is seen. In that case there are 3 possibilities.
1. ectopic pregnancy - usually diagnosed by following the beta-HCG numbers every 48 hours and not seeing them rise normally and not seeing an IUP
2. an earlier gestational age then expected, if the ovulation
occurred 2-4 weeks later then usual, this can sometimes happen especially as women get into their 40s, the ovulation can sometimes come later then usual randomly
3. a non-viable pregnancy, this is the most likely situation; at age 42 the risk of a non-viable pregnancy is about 30-40%, sometimes the beta-HCG will continue to rise despite the embryo
not growing normally
If nothing further is done and trek continues the risks for each of those situations would be as follows:
1. ectopic pregnancy becomes symptomatic and ruptures
2. pregnancy continues and is dealt with upon return from the trip
occur at some point
Yes it is quite possible that the beta-HCG can still rise some even after the pregnancy is not viable or disrupted.
It would be helpful to have the dates the beta-HCGs were drawn and the results for further analysis of the situation.